Dr. Awanish

EFFECT OF SO POLLUTION

ON PLANTS & ITS AMELIORATION

2

Associate Professor , Department of Botany M.G. P.G. College, Gorakhpur

www.learningmedia.in

8449001390, 9791976106

250

EFFECT OF SO POLLUTION ON PLANTS & ITS AMELIORATION2

The views expressed by the authors are their own. The editors and publishers do not ownany legal responsibility or liability for the views of the authors, any omission or inadvertenterrors.No part of this book may be reproduced or transmitted by any means/forms,electronic,mechanical, or any other way, without prior written permission from the publishers. Any dispute arising due to any issue/issues related to the publication of this book shall besubject to the jurisdiction of Meerut Courts only.

First Edition : 2020 ISBN: 978-81-942503-3-3

Contents1. Introduction 1-4

2. Morphological Effects of Sulphur Dioxide Pollution 5-8

3. Effects of Sulphur Dioxide on Plant Growth 9-13

4. Effects of Sulphur Dioxide on Flowering, Fruiting and Seeds 14-16

5. Physiological and Biochemical Effects of Sulphur Dioxide 17-26

6. Amelioration of Sulphur Dioxide Phytotoxicity 26-28

7. References 29-40

IntroductionThe organisms and their environment together

constitute an ecosystem. Both components of

ecosystem maintain a balance. Smaller or to some

extant even larger changes occurring in the ecosystem

get adjusted by reciprocal changes in one or the other

component. However, very large changes destroy the

balance of ecosystem; the control of one component of

ecosystem over the other gets lost. Environmental

resistance to these changes fails to work and thus a

state of disturbance is produced. This disturbed state

of the environment is called pollution. In a broad

sense, therefore, any unwanted and undesirable

change in physical, chemical and biological

characters of ecosystem is called pollution. As a result

of pollution human life, plant life, useful organisms,

living conditions, raw materials, environment, etc.

are irreparably damaged and may even be destroyed

permanently. Environmental pollution may be of

different types i.e. air pollution, water pollution, soil

pollution, noise pollution, radioactive pollution, etc.

Among these, air pollution is one of the most

hazardous to health of all organisms. Air pollution is

the transfer of harmful amounts of natural and

synthetic materials into the atmosphere as a direct or

indirect consequence of human activity. Common air

pollutants are liquid aerosol, SPM, oxides of sulphur

(SOx), oxides of nitrogen (NOx), compounds of carbon

(CO, CO2), ozone (O3), peroxyacetyl nitrate (PAN), etc.

INTRODUCTION

1

@ Introduction

Chapter Content

Effects of SO2 Pollution on Plants and Its Amelioration

Amongst these air pollutants, SO2 is one of most toxic air pollutant and major sources of SO2

emission are automobile exhaust, burning of fossil fuels in thermal power plants, smelting

industries, other processes such as manufacture of sulphuric acid and fertilizers and refining of

crude petroleum.

The problem of atmospheric pollution is rapidly growing in most parts of the world due to

human activity. The steadily growing demand for energy and excessive use, misuse, and

mismanagement of biosphere and other natural resources is the main cause of air pollution

problem. SO2 is the most common air pollutant, which causes damage to plants growing in

vicinity of SO2 producing sources. Sulphur dioxide contributes as much as 29% of air pollution.

Observation suggested that SO2 is next only to carbon monoxide (Neelu and Manju, 1997). The

Indian national ambient quality data indicate that emissions of a range of air pollutants are

generally increasing. The annual average of SO2 concentration ranged from10.4 to 39.0 ìg m-3 in

most part of country (Singh et al., 2005). The burning of coal and petroleum contributes the

greatest proportion of man made emission of SO2. India is the one of top three countries that

uses maximum fossil fuels (Jeyakumar et al., 2003).

SO2 is a colourless, poisonous gas with a characteristic pungent, chocking odour. It is highly

soluble in water and 2.2 times heavier than air. In presence of moisture, it gives nascent

hydrogen that reduces plant colouring material to colourless reduction product. Besides SO2

other oxides of sulphur such as sulphur monoxide (SO), sulphur dioxide (SO2), sulphur trioxide

(SO3), sulphur tetraoxide (SO4), sulphur sesquioxide (S2O3) and sulphur heptaoxide (S2O7) and

their corresponding acids and salts create severe air pollution.

The SO2 may be oxidized to SO3 and be precipitated as H2SO4 (this phenomenon is known as

acid rain). SO2 corrodes metals, tones leather, paper and fabrics. In our country there has been a

controversy in establishing crude oil refinery at Mathura because the smoke emitted from it

may affect the shine and dignity of Taj Mahal at Agra due to acid rain.

Sulphur (S) is one of the essential elements of plants required for growth and reproduction.

Sulphur is present in many biologically active compounds such as methionine, cystyine,

coenzyme A, thiamine and many others. Plant roots can absorb sulphate anions (SO42-) from the

soil; alternatively, leaves can absorb sulphur dioxide (SO2) from the atmosphere. When soil

sulphur is inadequate, atmospheric SO2 can be used as an alternate sulphur source. However,

uptake of excess sulphur from the soil or the atmosphere, or a combination of the two can result

in injury to vegetation.

When exposed to air pollutants the amount of pollutant that enters the plant has the

greatest effect on the degree of injury. In addition, many biotic and abiotic factors play a role in

the degree of damage when plants are exposed to SO2. Biotic factors include growth stage,

genetic make-up, plant nutrient status, insects, and disease. Abiotic factors include light,

moisture availability, temperature, relative humidity and the presence of other air pollutants.

The major route of atmospheric gases, including SO2, into plants is through the stomata

(apertures in the leaf epidermis, which can open and close to control gas exchange). When

exposed to SO2, some plants close the stomata thus reducing SO2 uptake, but not all plants close

their stomata upon exposure (Black, 1985). Water stress can also result in reduced stomatal

2

opening, which would result in reduced SO2 uptake. In order to enter through open stomata, SO2

must first diffuse across a layer of “unstirred” air surrounding the leaf called the boundary

layer. Increased air movement can decrease the diffusive resistance of the boundary layer

resulting in increased SO2 uptake.

After absorption, SO2 dissolves in the aqueous phase of the cell wall to form bisulphite

(HSO3-) or sulphite (SO32-), which then undergoes enzymatic conversion to SO42-. The SO42- is

then transported into leaf cells where it is incorporated into organic molecules, including amino

acids such as cysteine and methionine, which are then incorporated into proteins. When excess

SO2 enters the plant the resulting injury may:

¡ become visible as foliar injury (e.g. necrotic or dead tissue, chlorosis)

¡ result in disruption of metabolic or physiological processes, which lead to growth and yieldreductions

¡ result in accumulation of excess sulphur in plant tissues.

Plant growth and yield is the final end product of a series of biochemical and physiological

processes related to uptake, assimilation, biosynthesis and translocation of solutes.

Experimental studies have revealed that sulphur dioxide affects most of these processes leading

to considerable loss in crop productivity (Rao et al., 1985).

In most of the species, leaf areas collapse under intense exposure to sulphur dioxide.

Initially, the affected areas appear dull or water-soaked, later changing to a whitish yellow

colour due to bleaching and drying. In some species infected leaf areas appear brown or

brownish red in colour. Exposure to sublethal concentrations of sulphur dioxide causes

yellowing of green leaves. Chronic sulphur dioxide injury resembles the chlorotic symptoms of

higher plants. The affected areas may later change to a brownish red colour. The chronic

symptoms may start slowly with bleaching of chlorophyll until most of the pigments are

destroyed and interveinal leaf areas are nearly white. Leaf tissues may not collapse at this

stage, but by this time, the leaf itself may be abscised and lost.

Physiological injury is characterized by modification of physiological process such as

photosynthesis, respiration, diffusion, resistance of gases through stomata etc. Biochemical

injury may include inactivation of enzymes, change in inorganic and organic ingradients of

plants which leads to alteration in amount of carbohydrate, ascorbate, proline, phenolics, etc.

In a report of Whitercourt Environmental study group (1973), sulphur dioxide

symptomatology has been divided in to three types: transient, chronic and acute. This division

appears to be much more realistic, since it describes symptoms in terms of longevity as well as

degree of damage. It works well in describing the status of vegetation exposed to sulphur gas

emission under field conditions.

The degree of sulphur dioxide injury in plants varies with the time of the day. Because

stomata are the main avenues through which pollutants diffuse, sulphur dioxide injury occurs

mainly during the day, when the stomata are open. Some sulphur may also enter through the

cuticle. The sensitivity of plants to sulphur dioxide varies seasonally and is not the same

throughout the year (Cormis, 1973). The physiological conditions and maturity of leaves are also

important factor in determining the plant responses to sulphur dioxide. The recently matured

leaves are the most susceptible to sulphur dioxide injury (Workshop report, 1976).

Introduction 3

The response of a plant towards exposure of SO2 for a given period of time is determined by

the genetic make up of the plant species, physiological state of the plant and other

environmental factors. SO2 has proved to be highly influential upon the qualitative and

quantitative performance of the crop plants and forests. The high susceptibility of various traits

of the economically important crops and other plants has opened new vistas for research.

As the total control of SO2 air pollution is technically and economically not feasible, various

crop management practices , such as nutrient supplementation and spraying of chemical

protectants, such as growth regulators, antioxidants is suggested to be a short-term solution to

reduce the risk of air pollution damage (Rao et al., 1985; Singh et al., 2005). Researchers have

suggested that application of mineral nutrients promotes growth and pollutant injury to crops

(Rajput and Agrawal, 1994). Winterhalden (1981) suggested that Ca++ as mineral nutrient

provides the protection to SO2 exposed plants. Calcium hydroxide spray checks chlorophyll

degradation by neutralizing the acidity of SO2 in plants (Nandi et al., 1984). Shimazaki et al.

(1980) have found that chlorophyll breakdown in SO2 exposed plants can be checked by using

various free radical scavengers like sodium benzoate. Vitamin C (ascorbate) is an antioxisant

and has high oxygen radical absorbance capacity (ORAC) value, which helps in amelioration of

SO2 phytotoxicity (Singh et al, 2004). Han (2001) observed the relation between tree stomatal

infiltration and SO2 injury and the protection effect of ABA.

4

IntroductionThe importance of sulphur as plant nutrient dates

back to 1860 when Sachs and Knop established its

essentiality for plant growth. Sulphur content of

healthy leaves usually ranges from 500 to 14000 ppm

on dry weight basis (0.5 – 14 mg/g dry weight)

(Varshney and Garg, 1979). Plants usually absorb

sulphur from soil in the form of sulphate ions.

Sulphur can also be absorbed through leaves in the

form of sulphur dioxide (SO2) and sulphur trioxide

(SO3) from the atmosphere. Assimilation of sulphur

beyond a certain critical level adversely affects

photosynthesis, respiration and other plant processes.

On the basis of experimental exposures, a

concentration of about 429 ìg sulphur dioxide per m3

(0.15ppm) has been widely accepted as a threshold

level below which a range of higher plants would not

be injured even during prolonged exposure (Zahn,

1963). High levels of sulphur dioxide in the

atmosphere can increase the sulphur content in the

leaves beyond the critical level so that prolonged

exposure may cause irreversible injury and ultimately

death of the plant. Depending upon the concentration

and duration of exposure, plant responses to sulphur

dioxide are classified into three categories: acute

injury, chronic injury and physiological and or

biochemical injury (Severson, 1975).

MORPHOLOGICAL EFFECTS OF SULPHUR

DIOXIDE POLLUTION

2

@ Introduction

@ Morphological Effect

@ Visible injury

Chapter Content

Effects of SO2 Pollution on Plants and Its Amelioration

Acute injury is caused by the rapid absorption of sulphur dioxide in toxic concentration over 1.0 ppm

for short duration while chronic injury results from a prolonged exposure of plants to sublethal

concentration of less than 0.2ppm of sulphur dioxide or between 0.2 and 1.0ppm, usually lasting for

several days or weeks (Legge et al., 1976).

Morphological EffectsGaseous sulphur dioxide diffuses in the leaf mainly through stomata, though small amounts

may also be absorbed by the cuticle and absorbed in mesophyll. Once inside the leaf the sulphur

dioxide or its breakdown products react with cellular components, mainly cellular membranes

causing injury or death to tissues (Richard, 1965). Toxicity is due to reducing property of gas

(Varshney and Garg 1979; Jeyakumar et al., 2003; Bo Li et al., 2007 and Surowka et al., 2007).

When the concentration of SO2 increases, the cells are first inactivated with or without

plasmolysis, then killed, the tissue collapse and dry up, leaving the characteristic pattern of

interveinal and marginal acute injury. If only a few cells in an area are injured, this area may

become chlorotic or brownish red in colour, owing to chronic injury (Thomos, 1961, Ichikawa et

al., 1981).

Injury of sulphur dioxide is local. No systemic effect has been observed while the injured

areas of leaves never recover; the uninjured areas quickly and fully regain their functions and

new leaves develop normally (Thomos, 1961). SO2 pollution adversely affects the plants in term

of foliar injury in the form of chlorosis and necrosis, decrease in phytomass accumulation

(Shahare and Varshney, 1994), considerable reduction in shoot length, decrease in root number

and stomatal frequency and reduction in size of stomata (Jeyakumar et al., 2003).

Visible InjurySymptoms of SO2 injury can be described as either acute or chronic. Acute injury results from

short-term exposures to high concentrations that result in cellular death of all or part of the

plant. Chronic injury is the response to long-term exposures to sub-lethal concentrations that

result in alterations in cellular metabolism and may or may not exhibit visible injury (Legge et

al., 1998).

The foliar injury in sulphur dioxide treated plants is caused by accumulation of sulphites in

the mesophyll tissues of leaves which causes destruction of chloroplast and eventually leads to

interveinal necrosis (Thomos, 1961 and Rao et al, 1985). Mature leaves (middle and lower) were

more susceptible to sulphur dioxide injury, an observation also made by Biggs and Davis (1981).

This may be due to increased intercellular spaces in mature leaves which facilitate rapid gas

flow (Evans and Ting, 1974).

O’Connor et al. (1974) tested 131 native Australian plant species to determine their

sensitivity to acute SO2 exposure. Plants were exposed to 800 ìg m-3 SO2 for 27 h, 2,620 ìg m-3 SO2

for 3 and 6 h, 5,240 ìg m-3 SO2 for 4 h or 7,860 ìg m-3 SO2 for 0.5, 1, 2, 4 and 6 h. The measure of

sensitivity used was the percent of necrotic leaf tissue that had developed 3 or 4 days after

fumigation. It was observed that most species showed increased sensitivity with increased

6

concentrations of SO2 or with increased exposure times. Also, injury occurred most rapidly and

extensively to fully developed actively-photosynthesising leaves while young expanding leaves

were more resistant. It was also noted that sensitivity of species within genera could be highly

variable in their response to acute exposure to SO2

Grzesiak (1980) reported sulphur dioxide induced leaf injury in sunflower, barley and maize.

Mishra (1980) reported that high concentration of SO2 causes detrimental effect on the plant

due to sulphur accumulation which is manifested by appearance of necrotic lesions.

Saxe (1983) observed that the green leaf area was reduced by SO2 in bean (Phaseolus

vulgaris) plants at more than approximately 250 ìg/m3 SO2 concentration and after

approximately three weeks of exposure. He also observed that number of leaves at the time of

emergence of successive leaves was not affected. Combining the damaged leaf area with green

leaf area at the time of harvest, he demonstrated that leaf growth was always the same in all

chambers. Thus SO2 (approximately 250 g/m3) reduced green leaf area by injuring existing

leaves, rather than inhibiting leaf emergence or development.

Rao et al. (1985) observed that interveinal foliar injury symptoms appear in sulphur dioxide

treated plant of Vigna sinensis at 45 days and at the time of final harvest, the extent of foliar

injury was 18%. The symptoms were chlorotic but later on these become necrotic.

Kumar and Singh (1986) reported that Vigna sinensis plants exposed to sulphur dioxide

show visible foliar injury after 10 days of fumigation when whitish yellow chlorotic patches

appeared in interveinal areas. On prolonged exposures, these patches become dark brown

bifacial necrotic lesions in 0.25 and 0.5 ppm exposures. They also observed that the injury was

mostly confined to mature middle and lower leaves.

Kumar and Singh (1988) observed visible foliar injury in two cultivars T-9 and PU-19 of

Vigna mungo after 20-25 days of exposure of SO2 in the form of chlorotic patches which become

necrotic on prolonged exposures. They found that these necrotic lesions were bifacial,

interveinal and dark in colour and injury was mostly confined to mature middle and lower

leaves. Cultivar PU-19 was more susceptible in terms of foliar injury. Tomar et al. (1993)

exposed Abelmoschus esculentus to sulphur dioxide and observed foliar injury.

Kropff (1990) observed visible injury (brown/red spots) in bean (Vicia faba L.) exposed to SO2,

which progressed from the oldest leaves upward and also resulted in some leaf abscission.

Clapperton and Reid (1994) collected genotypes of timothy (Phleum pratense) from two field

sites, located in the foothills of southern Alberta, 5 and 20 km from a gas plant. Plants were

screened for SO2 sensitivity in experiments conducted in closed fumigation chambers. In the

first experiment, plants were exposed to 393 to 524 ìg m-3 SO2. The experiment was terminated

after 3 weeks when sensitive plants developed chlorotic areas, browning of the leaves and dead

tissue. In a second experiment, plants were exposed to 170 ìg m-3 SO2 and the experiment was

terminated when plants showed the first signs of damage (after two weeks).

Surowka et al. (2007) reported that Mesembryanthemum crystallinum plants fumigated

with 1.0 ppm sulphur dioxide over 7 days did not show any necrotic spot at the end of the

Morphological Effects of Sulphur Dioxide Pollution 7

experiment while the plants exposed to 6.0 ppm sulphur dioxide show necrosis on the second

day of treatment.

Effects at Subcellular LevelsAt subcellular levels, swelling of stroma thylakoids or fret has been observed in Vicia faba

when exposed to 0.25ppm sulphur dioxide for 1 hour or more (Wellburn et al., 1972). Higher

concentration of sulphur dioxide or long period of exposure increases the swelling of granum

thylakoids, particularly in top and bottom stacks of the granum. Swelling of thylakoids caused

by exposure of 0.25 ppm sulphur dioxide for 1 hour is irreversible even after the treated material

is transferred in unpolluted atmosphere. The photosynthetic apparatus appears to be adversely

affected due to the changes resulting at subcellular level in chloroplast fumigated with sulphur

dioxide. Because of the destruction of chloroplasts, leaves become chlorotic (Wellburn et al.,

1972).

Low concentrations (10- 50 ppm aquous, 1 ppm of gaseous sulphur dioxide = 1000ppm of

aqueous sulphur dioxide) have no detrimental effect on pine niddle tissue. Chloroplast treated

with 100 ppm of aquous sulphur dioxide solution shows some disorganization, while those

treated with 500 ppm exhibit more significant changes at ultrastructural level for example the

swelling of thylakoid discs and disintegration of other intracholoroplast membranes resulting in

the formation of small vesicles (Malhotra, 1976). Geelani et al. (2007) observed significant

change in leaf ultrastructure like cellular collapse, plasmolysis and active mesophyll cell

collapse associated with cellular disorganization as well as destruction of inner structure and

formation of vesicular bodies at acute level of sulphur dioxide exposure of 1000 ppm.

8

IntroductionFaller (1971) reported that even under the

condition of normal sulphur nutrition, very low level

of sulphur dioxide can stimulate plant growth. He

suggested that sulphur dioxide serves as a source of

nutrient ‘S’ at low level and this may explain

stimulation in root and shoot length and plant height.

Stimulation of growth at low level of sulphur dioxide

has also been reported by Bennet et al. (1974).

However, in higher doses and duration of exposure to

SO2, growth was adversely affected

Ashenden and Mansfield (1977) recognized that air

movement could influence SO2 uptake into plants so

they investigated the influence of wind speed on the

effects of SO2 on perennial ryegrass (Lolium perenne

L.). Plants were exposed in wind tunnels to 288 ìg m-3

SO2 at two wind speeds, 10 and 25 m min-1. When

exposed to SO2 with a wind speed of 25 m min-1, there

were significant reductions in leaf area, root/shoot

ratio and dry weight of green leaf material, dead

leaves + stubble, total shoot and roots. In contrast, dry

weights of plants exposed with a wind speed of 10 m

min-1 were not significantly reduced but there was a

significant increase in the number of fully expanded

green leaves.

EFFECTS OF SULPHUR DIOXIDE ON

PLANT GROWTH

3

@ Introduction

@ Effect of Sulphur Dioxide on Plant

Growth

Chapter Content

Effects of SO2 Pollution on Plants and Its Amelioration

Effect of Sulphur Dioxide on Plant GrowthThey concluded that the greater sensitivity to SO2 exhibited at the higher wind speed was

probably a result of reduced boundary layer resistance of the leaf. Ashenden and Mansfield

(1977) and Bell et al. (1979) observed that sulphur dioxide induces more reduction in root than

shoot. Crittenden and Read (1979) observed that the shoot dry weight of Lolium multiflorum cv.

S 22 and Dactylis glomerata cv. S 143 was reduced by 30- 40 % after 8-10 weeks in unfiltered air

containing mean sulphur dioxide concentration of 50- 90 mgm-3.

Pandey et al. (1980) reported that the Raphanus sativus root growth increased in lower

concentration of sulphur dioxide but there was corresponding decrease in shoot growth.

However, in higher concentration there was reduction in both root and shoot growth. Grzesiak

(1980) reported significant reduction in fresh weight of green leaves, shoots and roots, root/shoot

ratio, leaf area and dry weight fraction of Nicotiana tabacum and Cucumis sativus after

fumigation with 0.02 ppm of sulphur dioxide for four weeks.

Mishra (1980) exposed plants of Arachis hypogea to sulphur dioxide concentration ranging

from 0.06- 1.0 ppm for four hours daily for six weeks and observed reduced net primary

productivity in concentration of 0.25 ppm and above but slight beneficial effect on plant

productivity was observed in concentrations lower than 0.25 ppm .

Prasad and Rao (1981) reported reduction in root and shoot length, number of leaves,

nodules, flowers and pods in Phaseolus aureus exposed to petrocoke pollution. Prasad and Rao

(1981) also observed the effect of sulphur dioxide pollution on phytomass and net primary

productivity of wheat (Triticum aestivum) plants and reported an initial increase in these

parameters. They interpreted their results in terms of energy budget of plants under sulphur

dioxide stress conditions.

Jones and Mansfield (1982) also studied the effect of sulphur dioxide on growth and

development of Phleum pratense under different light and temperature environment. The dry

weight of root was consistently reduced while that of shoot was maintained at expense of root.

Kumar et al. (1983) observed the effect of exposure of 2, 4, 6, 8 and 10 mg sulphur dioxide m-3 on

30 days old field grown Arachis hypogea seedlings and reported that the lower concentration (2

mg m-3) enhance the number and biomass of vegetative plants.

Ghouse and Khan (1984) studied growth responses of Raphanus sativus to 0.25 and 0.50

ppm sulphur dioxide and observed a slight stimulation in plant growth at low cumulative doses

but at higher cumulative doses, significant decrease was recorded.

Narain and Singh (1984) reported that 22.5, 40.5, 67.5 and 90.0 ppm cumulative doses of

sulphur dioxide on Triticale hexaploide cv. TL-419 resulted in reduction of plant height, root and

shoot length, average number of leaves and roots per plant. Kumar and Singh (1985) in Pisum

sativum also observed appreciable reduction in all plant growth parameters along with dry

weight fraction and net primary productivity when exposed to sulphur dioxide.

10

Rao et al. (1985) observed that in all the Vigna sinensis plant sets, the root and shoot length

increased with age but these increases in control plants were more than those in sulphur dioxide

treated plants. They also observed that in sulphur dioxide exposed plants the number of leaves

and nodules were less than those of control plant of Vigna sinensis. They observed significant

decrease in dry matter accumulation in sulphur dioxide exposed plants

Kumar and Singh (1986) observed that exposure of Vigna sinensis to sulphur dioxide led to

an initial increase in the plant height and root and shoot lengths. On prolonged exposure of SO2,

they observed reduction in all growth parameters. The decrease corresponded with increase in

SO2 concentration. Reduction in root and shoot length was associated with a marginal decrease

in the number of leaves in early stages of plant growth but in later stages the number of leaves

per plant was significantly reduced. The number of nodules in Vigna sinensis also decreased

significantly in sulphur dioxide fumigated plants and the decrease was up to 75% in 0.5-ppm

sulphur dioxide. Dry matter production was decreased in early stages of plant growth even at

concentration of 0.12 ppm. At higher cumulative doses reduction in dry matter production was

significant but there was slight recovery in large stage of plant growth. They also observed that

reductions in the root weight fractions were higher than shoot weight.

Kumar and Singh (1986) also observed that in sulphur dioxide treated Vigna sinensis plants;

the number of pods per plant, pod length, number of seeds per pod, seed yield per plant, 100 seed

weight and biological yield were significantly reduced. There was about 50% yield reduction in

0.5-ppm sulphur dioxide.

Coleman et al. (1990) presented results on the variability of biomass production for wild

radish (Raphanus sativus x raphanistrum) and cultivated radish (Raphanus sativus) cv. Cherry

Belle when plants were exposed to SO2. Plants were exposed in fumigation chambers during a

10 h light period to 262, 629 or 1,048 µg m-3 SO2 for 24, 30 or 35 days. They found that variability

associated with biomass production increased as SO2 exposure increased while biomass itself

was only significantly reduced in one experiment using Cherry Belle.

Kropff (1990) reported that fumigation of broad bean (Vicia faba L.) with 74 µg m-3 SO2, for

the growing season, resulted in a 9% decrease in total dry matter accumulation and a 10%

decrease in pod yield at the final harvest. When exposed to 165 µg m-3 SO2, dry matter was

reduced by 17% and yield was reduced by 23%. The author indicated that the loss of dry matter

production was primarily as a result of loss of green leaf area in exposed plants.

Qifu and Murray (1991) used potato (Solanum tuberosum) to study the interactive effects of

soil water stress and SO2. Plants were exposed to 288 or 786 µg m-3 SO2, for 105 days in closed

top field chambers for 4 h per day under well-watered or water stressed conditions. Exposure of

well-watered potato plants to 786 µg m-3 SO2 resulted in significant decreases in leaf (25%) and

tuber (35%) dry weight as compared to controls. In contrast, dry weight reductions of water

stressed plants did not usually occur when plants were exposed to SO2. It was suggested that

the reduced response of water stress plants when exposed to SO2 might be a result of increased

stomatal resistance in response to mild water stress that may have reduced SO2 uptake.

Effects of Sulphur Dioxide on Plant Growth 11

Open-top chambers were used to investigate the response of barrel medic (Medicago

truncatula Gaerm.) cv. Paraggio when exposed to SO2 (Murray and Wilson, 1991). Plants were

exposed to 107 to 1,349 µg m-3 SO2 for 4 h day-1, 7 d week-1 for 72 days. Growth was affected very

little at concentrations up to 314 µg m-3 SO2 (<10% reduction); however, at 668 µg m-3 SO2, there

was 40 to 50% reduction in growth. At 1,349 µg m-3 SO2, there was little or no growth.

Tomar et al. (1993) observed reduced growth and yield characters when Abelmoschus

esculentus plants were exposed to higher doses of sulphur dioxide. Similar result was reported

by Gupta et al. (1993) in Lagenaria siceraria at higher doses of sulphur dioxide.

Top-covered chambers were used to investigate visible injury, growth, and stomatal

resistance of soybean (Glycine max L.) cv. Buchanan when exposed to salt stress followed by SO2

or SO2 followed by salt stress (Qifu and Murray, 1994). Plants were exposed to 380 or 786 µg m-3

SO2 for 5 h per d, for 3 weeks followed by exposure to low (320 g/200 L) or high (540 g/200 L) salt

stress for an additional 3 weeks. The reverse conditions were also looked at. They found that

exposure to either concentration of SO2 alone resulted in a significant increase in shoot : root

ratio and significant decrease in leaf area, root and shoot dry weight and fresh weight of root

nodules. Exposure to high salinity after SO2 resulted in visible injury within 5 days, death of all

plants from the high SO2 treatment within 12 days, and death of half of the low SO2 treatment

plants by the end of 3 weeks. In contrast, when high SO2 exposure was preceded by low salinity

stress, the adverse effects of high SO2 were moderated for all growth variables.

Julkunen-Tiitto et al. (1995) observed the effects of SO2 exposure on growth in six clones of

willow (Salix mysrsinifolia). They found that willow exposed to 300 ìg m-3 SO2 produced a 14% to

48% greater phytomass (leaf, stem and root dry weights) as compared to control plants. This

increased growth was attributed to SO2 acting as an additional nutrient source.

Coleman and Connaughay (1995) analyzed the effect of sulphur dioxide on radish cv. Cherry

belle and suggested that changes in root : shoot ratio and leaf area ratio in response to sulphur

dioxide induced reduction in plant size and development.

Ashenden et al. (1996) conducted greenhouse studies of SO2 effects on growth of 41 British

herbaceous species to determine if the species differed in their sensitivity to SO2. Plants were

exposed to a constant background concentration of 262 ìg m-3 SO2 with peaks applied during

daylight. During the first 4 weeks, peaks were 524 ìg m-3 for 2 h, twice per week. For the next 3

weeks 786 ìg m-3 was applied for 3 h, 3 times per week. Finally, for the last 3 weeks peaks of 786

ìg m-3 were applied for 3 h, 5 times per week. These concentrations were chosen to maximize any

growth differences between the tested species. Of the 18 statistically significant responses in

terms of total dry mass reductions, there was an average decrease of 43%. The mean response of

all 41 species was a 25% decrease in total dry mass. Of the seven statistically significant

responses of total leaf area, there was an average decrease of 40%. The mean response for all 41

species was a decrease of 10% in total leaf area. For leaf area ratio (total leaf area:total dry

mass), there was an average increase of 45% for the 20 statistically significant responses and an

average increase of 23% for all 41 species. An average decrease of 36% in the root:shoot ratio

12

occurred due to SO2 exposure (for the 13 species with statistically significant responses);

whereas, for all 41 species the decrease was 14%.

Saquib and Khan (1999) observed that sulphur dioxide and other pollutants affected the

normal growth, development, fertilization and yield of oil in Brassica juncea var. T 59. Katiyar

and Dubey (2000) reported loss of dry weight and observed effect on other growth parameters in

Zea mays exposed to 343 mg m-3 of sulphur dioxide.

Reddy and Dubey (2000) fumigated five common tree species with sulphur dioxide for six

hours daily for 30 days. Recovery from pollution stress was followed by 30 days after

termination of fumigation. Sulphur dioxide induced dry weight decreases per unit area and

increase in leaf area ratio (LAR). Agrawal et al. (2003) observed that food production and its

quality decreased when plants were grown in air polluted areas. They monitored 6 hours mean

concentrations for SO2, NO2, and O3 and reported reduced biomass and yield in Vigna radiata,

Beta vulgaris, Triticum aestivum and Brassica compestris.

Singh et al. (2003) also observed adverse effect on various growth parameters such as plant

height, biomass, leaf area, net primary productivity etc. in wheat (Triticum aestivum L. var. HD

2329) grown in urban area of Allahabad city where major gaseous pollutants are SO2, NO2, and

O3. Rajput and Agrawal (2005) observed that sulphur dioxide and other pollutants affect plant

height, number of tillers, leaves, ears, seeds and water use efficiency in wheat plant.

Wahid (2006) observed that in air polluted areas agricultural plants grown in unfiltered air

and unchambered field plots (containing SO2, NO2, an O3) show reduced growth parameters

than plants grown in open top chambers with charcoal filtered air. These plants showed stunted

growth and accelerated rate of leaf senescence. He observed that mid season harvest of

10-week-old plants revealed reduced plant fresh weight (14-37%) and dry weight (15-35%) in

unfiltered air chambers compared to filtered air chambers. Grain yield recorded after a full

season of growth was dramatically reduced in unfiltered air chambers with 43% for Pasban-90,

39% for Punjab- 91 and 18% for Inquilab-91 compared with air filtered control plants.

Nutritional quality of seeds was also significantly reduced in plants grown in unfiltered air

chambers.

Tiwari et al. (2006) observed in Daucus carota var. Pusa kesar that shoot length, number of

leaves per plant, leaf area and root and shoot weight increased significantly upon filtration of air

containing SO2, NO2, and O3. Rai et al. (2007) studied the effects of ambient gaseous air

pollution on wheat (Triticum aestivum L. var. HUW-234) growing in a suburban area situated

in eastern Gangetic plain of India, using open top chambers. Mean concentrations of SO2, NO2

and O3 were 8.4, 39.9 and 40.1 ppb, respectively during the experiment in non filtered chambers

(NFCs). They observed that yield of plants increased significantly in filtered chambers (FCs) as

compared to those ventilated with ambient air (NFCs).

Rai and Agrawal (2008) reported effect of air pollutant containing SO2 on two cultivars of rice

(Oryza sativa L. cv. Saurabh 950 and NDR 97) and reported reduction in yield. Yield reduction

was higher in NDR 97 than in Saurabh 950.

Effects of Sulphur Dioxide on Plant Growth 13

IntroductionSaxe (1983) reported that SO2 promotes senescence

and did not affect times for flowering and fruit

emergence. But many workers observed that fruiting

and flowering in slight earlier in SO2 treated plants.

Singh and Rao (1982) have reported advance flowering

in Cicer arietinum and similarly Kumar and Singh

(1985) observed early flowering in Pisum sativum as a

result of SO2 pollution. Kumar and Singh (1986)

observed that the SO2 treated plants flowered 1-4 days

advance. Pod maturation was also slightly advanced in

0.25 and 0.50 ppm SO2 concentration. Murray and

Wilson (1991) observed significant reduction in

flowering in Medicago truncatula Gaerm. cv. Paraggio

when exposed to SO2. Krishnayya and Date (1996)

reported greater reductions in fruiting than in

flowering, suggesting that fruit abortion was high in

Trigonella foenum-graecum L. exposed to SO2. The effect

of SO2 on seed germination is dependent on type of

species and concentration of gas used. Prakash et al.

(1977) observed effects of 0.06 and 0.18 gram/m3 SO2 on

seed germination of Cicer arietinum, Dolichos lablab,

Lens esculentus and Pisum sativum and noted a

decrease in their germination percentage.

EFFECTS OF SULPHUR DIOXIDE ON

FLOWERING, FRUITING AND SEEDS

4

@ Introduction

@ Effect on Pollen

@

Chapter Content

Effect of Sulphur Dioxide on Flowering, Fruiting , Seeds 15

Gupta et al. (1993) treated the seeds of two cultivars of Lagenaria siceraria to 334, 667, 1234,

2001 and 2668 mg/m3 of SO2 and observed a decline in germination percentage, seedling

survival and seed vigour.

Effect on PollenVarshney and Varshney (1981) exposed chick pea (Cicer arietinum L.), nasturtium

(Nasturtium indicum L.), petunia, (Petunia alba Juss.) and spiderwort (Tradescantia axillaris

L.) pollens to a range of SO2 concentrations when dry (1,310 to 13,100 ìg m-3) or wet (26.2 to

2,620 ìg m-3) for 1 to 5 h, in sealed chambers. Germination of pollens under moist exposure

conditions was almost completely inhibited at 262 ìg m-3 SO2 for the four species (1 to 3% of

controls); whereas, dry exposure did not affect up to 7,860 ìg m-3 SO2. It was suggested that the

greater toxicity of SO2 to moist pollens was due to its conversion to sulphite (SO32-) or hydrogen

sulphite (HSO3-) ions. Moist exposure to SO2 also greatly reduced pollen tube growth. There

were reductions in pollen tube length from 5.5 to 28.5% after 1 h exposure to 26.2 ìg m-3 SO2 and

91.3 to 96.6% after 1 h exposure to 262 ìg m-3 SO2. Pollen fumigation under dry conditions

resulted in approximately 35% reduction in pollen tube growth for all species after 5 h exposure

to 13,100 ìg m-3 SO2. It was suggested that the reduction in growth was due to SO2 effects on the

generative nucleus.

Linskens et al. (1985) exposed petunia (Petunia hybrida Vilm.) pollens in vitro to 52,380 ìg

m-3 SO2. Pollen germination and tube growth were measured after 2 and 3 hours incubation,

respectively. There were significant reductions from the controls in both pollen germination

(45%) and tube length (32%). The reductions were attributed to reductions in pH (acidification)

of the medium.

Experiments in which Monterey pine (Pinus radiata) pollens were exposed to 262 to 26,190

ìg m-3 SO2 for 24 h resulted in noticeably reduced pollen germination and approximately 50%

reduction in pollen tube growth at 2,619 ìg m-3 SO2 (O’Connor et al., 1987). Chromatography

assays were also performed to determine the effects of SO2 on the metabolites of early

germination. It was found that percent activity was reduced by 24% (aspartate), 13%

(glutamine), 10% (alanine), and 26% (ã-amino butyrate) at 262 ìg m-3 SO2. In addition, the

number of identifiable metabolites was decreased. It was concluded that SO2 inhibited the

enzymes that catalyze the formation of the metabolites.

Vicia faba cv. Giza-2 plants were exposed to SO2 concentrations of 13,095 to 654,750 ìg m-3

for 5 h or 13,095 ìg m-3 for 5 h d-1 for 1, 2 or 4 days to determine if there were cytogenetic or

viability effects on pollen (Amer et al., 1989). The number of non-viable pollen grains increased

significantly as the concentration of SO2 increased. They used chromosome fragmentation as

the criterion for mutagenic potential. Statistical analysis of the results indicated that the

percentage of abnormal pollen mother cells (PMC’s) increased significantly after exposure to

13,095 ìg m-3 SO2 for 5 h and the percentage of abnormal cells increased as the concentration of

SO2 increased or as the period of fumigation increased.

Bosac et al. (1993) studied the effects of wet and dry exposure, both in vivo (on the anthers)

and in vitro (culture dishes) on germination of pollen from oilseed rape (Brassica napus) cvs.

Tapidor and Libravo. For in vivo treatments, inflorescences were exposed in special chambers

Effects of SO2 Pollution on Plants and Its Amelioration16

(excluding the rest of the plant) to 524 ìg m-3 SO2 for 6 h. In vitro exposures (either wet or dry)

were for 3 h. Exposure to 524 ìg m-3 SO2 had no effect on germination or pollen tube length, in

vivo or in vitro (dry); however, there was a significant reduction in germination when pollens

were exposed to SO2 while in unbuffered medium droplets. Pollen tube length was also greatly

reduced under these conditions but few pollen grains germinated and grew to calculate reliable

means.

Chauhan and Jain (1994) observed effect of various concentration of SO2 on pollen fertility in

Capsicum annuum L. var. Pusa jwala. The reduction in pollen fertility increased with the

increase in the concentration and period of fumigation. Maximum reduction in pollen fertility

(45%) was shown by plants fumigated with 1 ppm SO2 for 50 days at bud initiation stage.

Agrawal et al. (1995) utilized a nightshade (Solanum nigrum) complex, which exhibits three

natural cytotypes [diploid (S. americanum), tetraploid (S. villosum) and hexaploid (S. nigrum)]

to determine the effects of SO2 on pollen chromosomes. Flowering plants were exposed to 524 ìg

m-3 SO2 for 2 h d-1 for 3, 7 or 11 days. When pollen mother cells (PMC’s) were examined, it was

found that meiotic chromosomal abnormalities were highest in diploid plants (19.67 to 26.0%)

and least in hexaploid plants (4.45 to 7.0%). In addition, abnormalities increased with length of

exposure for all plants. Pollen sterility followed the same pattern as chromosomal

abnormalities, 19.5 to 21.6% in diploid, 13 to 15% in tetraploid and 10 to 13% in hexaploid, and

sterility increases with length of exposure. The authors concluded that the observed

abnormalities might have resulted from free radical splitting of phosphodiester linkages of DNA

or from bisulphite combining with cytosine or uracil which may result in alteration of DNA or

RNA functions.

IntroductionStomata are main avenues for diffusion of gases

and water vapor in plants. Any factor whichinfluences stomatal movement is likely it affect plantwater relation as well as diffusion of carbon dioxideand oxygen. Sulphur dioxide exerts a markedinfluence on the stomatal movement (Majernik andMansfield, 1970; Majernik and Mansfield, 1972;Unsworth et al., 1972 and Biscoe et al., 1973). It hasbeen observed that at 40% relative humidity and 180C,sulphur dioxide promotes stomatal opening, therebypromoting greater diffusion of sulphur dioxide intoleaves (Mansfield, 1970). The rate of opening ofstomata in light is faster in sulphur dioxide treatedplants than untreated plants. The size of stomatalaperture in sulphur dioxide treated plant isconsiderably larger and stomata take relativelylonger time for complete closure in the dark. Thestimulatory effect of 1 ppm of sulphur dioxide onstomatal opening is reversible but it becomesirreversible after six hours (Majernik and Mansfield,1970). It has also been observed that night opening ofstomata, a characteristic of broad bean plant, begins1 to 2 hours earlier and the stomata are more widelyopen in treated plants. Similar phenomenon has beenobserved in maize, barley and several other plantspecies (Majernik and Mansfield, 1970). Sulphurdioxide induced opening of stomata has greatphysiological and ecological implications. Prolongedopening of stomata results in excessive loss of waterthrough transpiration. Consequently the waterrequirement of the plant in sulphur dioxide pollutedareas will be relatively larger.

PHYSIOLOGICAL AND BIOCHEMICAL EFFECTS OF

SULPHUR DIOXIDE

5

@ Introduction

@ Effect on Stomata and Transpiration

@ Effect on photosynthetic pigmentsand Photosynthesis

@ Sulphur dioxide uptake and plantsulphur content

@ Effect on other metabolic processes

Chapter Content

Effects of SO2 Pollution on Plants and Its Amelioration

Any condition, which promotes stomatal opening, will enhance sulphur dioxide diffusionand damage; whereas the chemical which can nullify the sulphur dioxide induced stomatalopening may provide protection against sulphur dioxide pollution (Varshney and Garg, 1979).

Black and Black (1979) used light microscopy to examine epidermal strip taken frombean plants exposed either to normal or to polluted air. The enhanced opening response ofstomata induced by low concentration of sulphur dioxide was associated with extensivedestruction of adjacent epidermal cells whereas guard cell survival was not reducedsignificantly. Collapsed epidermal cells were also observed using scanning electron microscopyin intact leaf samples that were taken from Vicia faba polluted with sulphur dioxide. Thisevidence suggested that the enhanced stomatal opening in bean induced by low concentration ofsulphur dioxide might result from preferential injury to the adjacent epidermal cells. At highersulphur dioxide concentrations stomatal closure was observed and was found to be associatedwith cellular disorganization and reduced guard cell viability.

Saxe (1983) observed that in the early stage of experiment, transpiration increases butafter long-term exposure of sulphur dioxide, transpiration decrease due to reduction in leaf areaand permanent closure of stomata.

Effect on Stomata and TranspirationStomatal effects induced by sulphur dioxide are varied on magnitude and direction;

depending upon the species and environmental conditions, exposure to sulphur dioxide may

result in stomatal exposure, stomatal opening or no reaction on stomata at all (Black, 1985). In a

study designed to examine changes in leaf gas exchange resulting from SO2 exposure, Gerini et

al. (1990) exposed maize (Zea mays L.), in fumigation chambers to 113, 186 or 291 ìg m-3 SO2 for

4 weeks. He observed that stomatal conductance, transpiration rate and intercellular/ambient

CO2 were enhanced at the lowest SO2 treatment but then declined to near control levels at thehighest SO2 treatment. In contrast, water use efficiency and CO2 assimilation rate declined at

the lowest concentration and then increased (but not back to control levels).

Darrall (1991) utilized an open-air fumigation system to examine the effects of SO2 (ambient,

low, medium and high) on (Hordeum vulgare L.) cv. Igri and observed increased stomatal

conductance and transpiration at low level of SO2 and decreased stomatal conductance and

transpiration at high level of SO2.

Lorenzini et al. (1995) evaluated the gas-exchange response of two-year-old seedlings of oak

(Quercus pubescens Wild.) and Turkey oak (Quercus cerris L.) exposed to 73, 160 and 244 ìg m-3

SO2 for 23 weeks, in fumigation chambers. After 11 weeks of exposure, Q. pubescens exhibited a

significant linear decrease in stomatal conductance, transpiration rate and water use efficiency.

In addition, the vapour pressure deficit increased with increasing SO2 concentration and the

internal/ambient CO2 concentration ratio was not affected. For Q. cerris, there was a significantlinear decrease in vapour pressure deficit and water use efficiency, but there was no effect on

stomatal conductance or the transpiration rate. The internal/ambient CO2 concentration ratio

increased 15% at 244 ìg m-3 SO2.

Ranieri et al. (1999) observed reduced stomatal conductance (by 56% and 58%) in Hordeum

vulgare L. cv. Panda and Express respectively to long-term exposure of 210 ìgm-3 SO2 in a

greenhouse. Jeyakumar et al. (2003) observed that stomatal frequency and stomatal index were

not affected by sulphur dioxide. However the size of stomata was significantly reduced. Rajput

and Agrawal (2005) observed reduced stomatal conductance and water use efficiency in

18

Triticum aestivum var. HUW 468 after exposure of air pollutants containing SO2. Tanner et al.

(2007) observed in the plumes of actively out gassing vents of Kilauea volcano where

volcanogenic sulphur dioxide is high in comparison to control location; stomatal index of

Swordfern (Nephrolepis axaltata) was very low.

Geelani et al. (2007) observed that at 10 ppm of aqueous sulphur dioxide exposure, no stomatalopening was observed while at 100 ppm, stomatal opening were pronounced. Acute level ofsulphur dioxide exposure of 1000 ppm caused significant stomatal damage and reduced guardcell viability.

Effect on Photosynthetic Pigments and PhotosynthesisPhotosynthesis is one of the most fundamental biological processes through which

atmospheric carbon dioxide is fixed using solar energy. The photosynthetic process is highlysensitive to sulphur dioxide pollution. Sulphur dioxide alters the metabolic processes of plants(Zeigler, 1972; Wellburn, 1982) and decreases their photosynthetic activities (Silvis et al., 1975and Agrawal et al., 1991) and obviously yield and productivity (Godzik and Krupa, 1982; Kumarand Singh, 1985; Kumar and Singh, 1986; Chand et al., 1989 and Prakash et al., 1989).

The diverse effects of sulphur dioxide on photosynthesis is partly due to its action onphotosynthetic pigments. Sulphur dioxide absorbed in plants through stomata, combines withwater in intercellular spaces to form sulphurous acid, which dissociates in to H+ and HSO3

- ionsand cause degradation of chlorophyll by displacing Mg+2 ion from chlorophyll molecules andconverting them in to pheophytin, there by impairing photosynthetic activity of chlorophyllmolecules (Rao and LeBlanc, 1966).

Rao et al. (1985) studied the effects of 0.25 ppm SO2 on Vigna sinensis plants exposedwithin closed polythene chambers for 1.5 hours daily for 40 days (30-69 days old plants) andobserved that the chlorophyll a and chlorophyll b gradually increased up to 50- day age incontrol plants and decreased continuously in SO2 treated plants. The impact of sulphur dioxideon chlorophyll content is so definite and quantitavily related that chlorophyll content is evenconsidered as an indicator of sulphur dioxide pollution. Significant decrease in carotenoidcontent was also observed in 70-day old plants.

Taylor et al. (1986) investigated physiological differences of two ecotypes of geranium(Geranium carolinianum) that differed in their sensitivity to SO2. Inhibition of photosynthesisin the resistant ecotype was dependent on concentration but independent of time. From 3 to 5 hexposure, the percentage inhibition increased from an average of 11.5% at 786 ìg m-3 to 29.9% at1,571 ìg m-3 SO2. In contrast, photosynthesis in the sensitive ecotype was inhibited at allconcentrations of SO2. Percentage inhibition increased significantly with exposure time.Long-term exposure to 1,179 ìg m–3 SO2 for 6 h d-1, 4 d wk-1, for 4 weeks resulted in a 28%increase (resistant ecotype) and 26% decrease (sensitive ecotype) in photosynthesis fromcontrols. In addition, photoassimilate retention in the foliage was reduced by 6% in the resistant ecotype and increased by 7% in the sensitive ecotype.

Gerini et al. (1990) exposed maize (Zea mays L.) in fumigation chambers to 113, 186 or291 ìg m-3 SO2 for 4 weeks and reported 20% decrease in photosynthetic activity in plantsexposed to 113 and 186 ìg m-3 SO2. At 291 ìg m-3 SO2, photosynthetic activity was decreased by10% as compared to control plants. The decrease in photosynthetic activity was attributed toreduced mesophyll assimilation capacity.

Darrall (1991) utilized an open-air fumigation system to examine the effects of SO2

(ambient, low, medium and high) on photosynthesis and discussed observed changes in relationto grain yield in winter barley (Hordeum vulgare L.) cv Igri. Experiments were conducted for 3years and the SO2 concentrations varied within each year. The average concentrations for the

Physiological & Biochemical Effects of Sulphur Dioxide 19

highest SO2 treatment, for each year were 100, 113 and 126 ìg m-3. Although SO2 significantlyincreased net photosynthesis on some occasions, significant decreases were observed on otheroccasions. Most of the photosynthetic changes were transient and were attributed tosimultaneous changes in stomatal conductance and transpiration.

Montiel-Canobra et al. (1991) reported the effects of SO2 on photosynthetic carbonmetabolism in winter barley (Hordeum vulgare L.) cv. Igri in a 2-year field experiment. In thefirst year of the study, samples were collected from the ambient (18 ìg m-3) and high (126 ìg m-3)SO2 treatments and in the second year samples were collected from the ambient, medium (73 ìgm-3) and high (100 ìg m-3) SO2 treatments. Significant reductions in photosynthesis wereobserved. Exposure to the highest SO2 treatment in each growing season (100 and 126 ìg m-3),resulted in a significant reduction in fructose-1, 6-bisphosphatase (FBPase) activity beingobserved for the post-anthesis period. It was concluded that reductions in FBPase couldinfluence photosynthetic carbon partitioning in leaves, assimilate distribution and export offixed carbon to developing tissues. There were no significant effects on chlorophyll content,phosphoribulokinase (PRK), NADP-dependent glyceraldehyde-phosphate dehydrogenase(NADP-GPD) or phosphoglycerate kinase (PGK) in either growing season.

Veeranjaneyulu et al. (1991) used photoacoustic techniques (detection of heat andphotosynthetic O2 pulses from leaves) to study responses of photosynthetic activity (oxygenevolution and energy used in photosynthesis-PES) to 131 to 5,238 ìg m-3 SO2 in the broad-leaftree, sugar maple (Acer saccharum). They found that at 131 ìg m-3 SO2, O2-evolution and PESincreased by 65% and 24% respectively. However, at 5,238 ìgm-3 SO2, these two parametersdecreased by 50% and 22% respectively as compared to controls. It was concluded that theenhanced O2 evolution and PES observed at the lowest concentration was a result ofdetoxification of SO2, which inturn stimulated photosynthetic electron transport and that thehigher SO2 concentrations inhibited this electron transport reduced O2 evolution and PES.

To determine the effect of SO2 on chlorophyll content, Panigrahi et al. (1992) exposed rice(Oryza sativa L.) at 20, 40, 60, 80 and 100 days age; and mung bean (Phaseolus aureus R.) cv.Dhauli at 15, 30, 45 and 50 days age to 655 to 5,240 ìg m-3 SO2 for 6 to 48 h. For both species,chlorophyll content decreased significantly with increased SO2. In addition, chlorophyll contentdecreased in each SO2 treatment as the exposure time increased. It was found that chlorophyllcontent decreased between 20 and 40% in rice and mung bean at SO2 concentrations of 655 and1,310 ìg m-3 respectively. Exposure to the highest concentration of SO2 (5,240 ìg m-3) resulted inalmost complete destruction of chlorophyll. It was concluded that a decrease in chlorophyll leads to a decrease in photosynthesis, NPP and other growth parameters.

Lorenzini et al. (1995) exposed two-year-old seedlings of oak (Quercus pubescens Wild.)and Turkey oak (Quercus cerris L.) to 73, 160 and 244 ìg m-3 SO2 for 23 weeks, in fumigationchambers and observed significant linear decrease in photosynthetic activity in Q. pubescensand Q. cerris.

Ranieri et al. (1999) investigated long-term exposure of barley (Hordeum vulgare L.) cvs.Panda and Express to 210 ìg m-3 SO2, in a greenhouse, to establish if negative impacts of SO2

could be linked to specific changes in the photosynthetic apparatus. The 75 day exposure to 210ìg m-3 SO2 decreased photosynthetic activity by 29 and 49% in cultivars Panda and Express,respectively. Whole electron transport chain activity was reduced by 27% (Panda) and 29%(Express). Electron transport activities of photosystem I and II were reduced by 7 and 11%,respectively, in Panda and 18 and 24% respectively, in Express. Significant decreases in leafpigments were also observed. For example, chlorophyll a decreased by 44% (Panda) and 10%(Express), while carotenoids decreased by 46% (Panda) and 10% (Express). Pigment-proteincomplexes from thylakoid membranes did not show any qualitative or quantitative differencesbetween control and SO2 exposed plants. The authors concluded that the reduction in

20

photosynthetic activity could be attributed to stomatal closure and a generalized negativeimpact on the photosynthetic apparatus.

Jeyakumar et al. (2003) reported reduced chlorophyll contents and hence reducedphotosynthesis in Zea mays exposed to SO2. The enzyme chlorophyllase is responsible fordegradation by removal of phytol or reversible reaction. Sulphur dioxide pollution increases thechlorophyllase activity so decrease in chlorophyll contents was observed.

Sharma and Tripathi (2008) observed the effect of ambient sulphur dioxide, nitrogendioxide, suspended particulate matter (SPM), respirable suspended particulate matter (RSPM), dust-fall rate (DFR) on two most common tree species, Ficus benghalensis L. (Evergreen tree)and Dalbergia sisso Roxb. (Deciduous tree). Considerable reduction in photosynthetic pigments(chlorophyll a, chlorophyll b and carotenoids) and sugar contents were observed at sitesreceiving higher pollution load.

Sulphur Dioxide Uptake and Plant Sulphur ContentWhen exposed to SO2, there can be wide variation in the absorption and accumulation of

sulphur compounds between plant species. In some species foliar sulphur and sulphate content

may be used as an indicator of SO2 exposure. Clarke and Murray (1990) observed long-term SO2

exposure effects on Eucalyptus rudis Endl. There was no effect on S content at the lower

concentration of SO2, but the 274 ìg m-3 treatment significantly increased total leaf S.

Rao and Dubey (1990) observed that sulphate accumulation in the leaves correspond with

the ambient SO2 level. When exposed to 90 ìg m-3 SO2, the sulphate content in the leaves

increased by 72%, 69%, 65% and 92% for ber, jamun, neem, and mango respectively, in

comparison to the control site. Increased sulphate content in the four species ranged from 26%

to 48% at the site with an ambient level of SO2 (48 ìg m-3).

Qifu and Murray (1991) reported increased sulphur content in potato (Solanum tuberosum)

exposed to different concentration of SO2. At harvest, the leaf S content of well-watered plants

had increased by more than 100% and 125% in the 288 and 786 µg m-3 SO2 treatments,

respectively. When water stressed, the lower SO2 treatment had little effect on S content;

whereas, the 786 µg m-3 treatment resulted in a 100% increase in leaf sulphur.

In an attempt to assess the critical level of SO2 in the air which would cause adverse effects

on vegetation, Manninen and Huttunen (1995) examined total sulphur content in needles of

Scots pine (Pinus sylvestris L.) growing at ambient SO2 levels. Monthly mean concentrations

ranged from 10 to 100 ìg m-3 in 1980, 8 to 61 ìg m-3 in 1985 and 0 to 95 ìg m-3 in 1989. They found

significant correlations between total sulphur content of the two youngest age-classes of needles

(7 and 19 months).

The Liphook Forest Fumigation Project was established to determine the long-term effects of

exposing specific tree species to realistic levels of SO2 and O3 within field fumigation plots. One

of the studies investigated sulphur and nutrient accumulation in needles of Sitka spruce (Picea

sitchensis Bong. Carr.), Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L.

Karst.) exposed to 34 or 58 ìg m-3 SO2 for 43 months (Shaw and McLeod, 1995). In all three

species, both SO2 concentrations resulted in increased sulphur content and ratio of sulphur to

cation levels, in exposed needles.

Agrawal and Singh (2000) studied six species of tropical trees from a low rainfall area along a

pollution gradient (seasonal average of 49 to 233 ìg m-3 SO2) around two coal-fired power plants

Physiological & Biochemical Effects of Sulphur Dioxide 21

in India. Two species of evergreens (mango, Mangifera indica; eucalyptus, Eucalyptus hybrid)

and four species of deciduous trees (guava, Psidium guajava; cassod tree,Cassia siamea;

flame-tree, Delonix regia; bougainvillea, Bougainvellea spectabilis) were studied. Total foliar

sulphur content was higher in all six species at the most exposed location compared to the

reference location. In deciduous species, there was a greater increase in the foliar sulphate-S

content after the onset of new leaves during the summer, which was possibly due to

translocation of sulphur from woody plant parts.

Dwivedi et al. (2008) studied the relationship between ambient air sulphur dioxide andsulphate content in leaf of selected Ficus religiosa. The study reveals a positive correlation

between ambient air sulphur dioxide and sulphate in the leaves. Two ways ANOVA finds the

obtained values to be highly significant (p < 0.001). Amount of sulphate in leaves shows positive

correlation with sulphur dioxide in air (p < 0.001) during most part of the study. A marked

reduction of sulphate content in leaf was found during October when reduction in ambient air

sulphur dioxide was recorded.

Al Sayegh Petkovsek et al. (2008) reports the amount of total sulphur content analyzed in

needles of Norway spruce (Picea abies L.) in the area influenced by sulphur emissions from the

Sostanj Thermal Power Plant (STPP), Slovenia, in the period 1991-2004. After desulphurization

of emission gases from STPP, total sulphur content in needles decreased and vitality

parameters of needles increased. They found a strong correlation between the average annual

emissions of SO2 from STPP and average annual sulphur content (increase) in needles. The

results showed that spruce needles may be a useful bioindicator for detecting changes in the

emission rates of SO2.

Effect on other Metabolic ProcessesExposure of plants to SO2 can result in disruption of normal metabolic activity. Enzymatic

activity can be increased or decreased or photosynthesis and respiration can be altered. The

degree of metabolic change is dependent on the concentration of SO2 and the length of exposure.

It is possible that metabolic disturbance can occur without visible signs of injury.

Horsman and Wellburn (1977) used Rumex obtusifolius collected from areas of high ambient

(annual mean 150 ìg m-3) and low ambient (30 ìg m-3) SO2 to determine effects of SO2 exposure on

enzyme activities. Plants were fumigated with 524 ìg m-3 SO2 for 11 days in a wind-tunnel

fumigation system. Ribulose-diphosphate carboxylase (RuDPC) in low ambient area leaves wasreduced to 65% (young) and 68% (old) of controls. Fumigated high ambient plants exhibited

little change in RuDPC in either young (97%) or old leaves (109%). Peroxidase levels in the low

ambient plants increased following exposure (140% young leaves, 135% old leaves). The high

ambient area plants had significantly higher levels of peroxidase (>140%) than low ambient

plants under control conditions and experienced relatively small changes in peroxidase

following SO2 exposure (114% young leaves, 105% old leaves). Glutamate-pyruvate

transaminase (GPT) and glutamate-oxaloacetate transaminase (GOT) levels increased in

fumigated young leaves (138% and 127% low ambient; 119% and 123% high ambient), from both

areas, while old leaves were not affected. It was concluded that the differences in enzyme

activities between low and high ambient plants could be a result of development of sulphite

tolerance in the high ambient plants and could be the reason for maintenance of RuDPC

22

activity. The high activity of peroxidase in high ambient plants could reflect adaptation to the

SO2 levels of their natural environment.

Tanaka and Sugahara (1980) used Populus euramericana and Spinacia oleracea L. cv. New

Asia to show that increased resistance to SO2 can be correlated with high levels of superoxide

dismutase (SOD) activity in leaves. They observed that young poplar leaves had up to five times

more SOD activity than old ones when exposed to 5,238 ìg m-3 SO2 for 22 hours. The higher SOD

activities resulted in reduced chlorophyll destruction and lower malondialdehyde formation (a

product of lipid peroxidation). In order to confirm the role of SOD in reducing SO2 toxicity,

diethyldithiocarbamate (DDTC, a SOD inhibitor) was applied to spinach leaves. This resulted in

65% reduction in SOD activities after 2 h exposure. Exposure of spinach leaves that had been

treated with DDTC to 1,310 ìg m-3 SO2 for 22 h resulted in enhanced chlorophyll destruction

over untreated leaves. In addition, it was shown that pretreatment of poplar leaves with 262 ìg

m-3 SO2 for 20 days increased SOD activities to 4.4 times the control. Shimazaki et al. (1980)

presented further evidence that SOD plays a role in SO2 resistance.

Nandi et al (1982) exposed field grown rice (Oryza sativa L.) plants separately to 0.25 or 0.5

ppm SO2 for 1.5 hr daily for 40 days, showed significant decrease of catalase (p < 0.001) and

increase of peroxidase (p < 0.001) activities as well as decreases of protein (p < 0.001) and

ascorbic acid (p < 0.001) contents associated with leaf lesions, which were proportional to

SO2-dose. Catalase and peroxidase activity levels showed an inverse relationship. It is

hypothesized from the molecular structure of both enzymes and from the in vitro relationship

between catalase and peroxidase activity that the tetrameric molecules of catalase in vivo might

disintegrate into monomeric units with peroxidase activity, which in turn oxidize ascorbic acid

and may reduce tolerance of plants to SO2.

Rao and Dubey (1990) studied antioxidant production and its role in protecting four tropical

tree species (ber, Zizyphus mauritiana; jamun, Syzygium cumini; neem, Azadirachta indica;

mango, Mangifera indica) from air pollution. Four exposure sites were selected downwind from

an industrial source, while the control site was 10 km upwind. Samples were collected once a

month for 12 months. The monthly average SO2 concentration at the 4 sites ranged from 48 to 90

ìg m-3. Oxidation of proteins, superoxide dismutase activities and peroxidase activities

increased in all four species. The magnitude of the response varied with species and was related

to the ambient SO2 concentration. It was concluded that increased peroxidase and superoxide

dismutase activities could increase SO2 tolerance under field conditions.

Chauhan (1990) performed a study on the early diagnosis of SO2-stress and the mechanism

of SO2 damage in crop plants by measuring volatile emissions from treated tissues. Emissions

from tomato (Lycopersicon esculentum Mill.), mung bean (Vigna radiata L.) and maize (Zeamays L.) were measured after exposure to 262 ìg m-3 for 2 h per day or 524 ìg m-3 for 1 h per day

till maturity. Ethylene, ethane, acetaldehyde, and ethanol were measured at 15 day intervals.

Ethylene emissions increased substantially in all three species, until visible injury symptoms

(chlorosis followed by necrosis) appeared, after which ethylene declined until the end of the

exposure. Ethane emissions were detected just prior to the appearance of visible injury

symptoms and increased as injury increased. It was suggested that ethane production was a

result of lipid peroxidation caused by sulphate oxidation. To verify this, an additional

experiment with mung bean was performed to establish if the addition of antioxidants would

Physiological & Biochemical Effects of Sulphur Dioxide 23

reduce SO2 induced damage. Antioxidants substantially reduced ethylene and ethane

production supporting the idea that lipid peroxidation was caused by free radicals resulting

from sulphite oxidation. Acetaldehyde and ethanol emissions increased as exposure duration

increased up to 45 days, but emissions declined after the appearance of visible injury symptoms.

As acetaldehyde and ethanol are not normal by-products of aerobic metabolism the author

suggested that their production was a result of SO2 alteration of respiratory metabolism. The

rates of emissions of ethane, acetaldehyde, and ethanol were related to the degree of SO2

resistance displayed by the species in the study (the greater the resistance, the greater the rates

of emissions).

Gupta et al. (1991) studied the effects of SO2 exposure on soybean (Glycine max) cv. Elf to

determine effects on abscisic acid (ABA) content at the end of the exposure period and after a

recovery period of 18 hours. Thirty day old soybean seedlings were exposed in growth chambers

to 131, 524 or 1,048 ìg m-3 SO2 for 1, 2 or 4 hours. They found that both exposure concentration

and duration significantly increased abscisic acid (ABA) content in leaves. At a SO2

concentration of 131 ìg m-3, ABA content increased 28% after 1 h, 87% after 2 h and 141% after 4

h exposure. The 18 hour recovery period resulted in a reduction of ABA levels in all treatments,

but ABA levels were still higher than the controls.

Madamanchi and Alscher (1991) examined antioxidants and antioxidant enzymes in an

attempt to understand the metabolic differences of two cultivars of pea (Pisum sativum L.)

known to differ in their sensitivity to SO2 exposure (cvs. Progress, insensitive and Nugget,

sensitive). Plants were exposed in continuously stirred tank reactors to 2,095 ìg m-3 for 210 min

after SO2 reached the target concentration (this took about 40 min.). Total glutathione (ratio of

exposed/control) content increased from 1.11 (at 0 min.) to 2.04 (at 210 min. exposure) inProgress and 1.42 (at 0 min.) to 1.69 (at 210 min. exposure) in Nugget. Reduced glutathione

(GSH) increased in Progress from 1.11 to 1.93 and in Nugget from 1.37 to 1.59 for 0 and 210

minutes exposure, respectively. No significant effects were found on ascorbic acid or oxidized

glutathione content. Superoxide dismutase activity increased 90% in Progress, but was

unaffected in Nugget. Mean glutathione reductase activity increased 35% and 21% in Progress

and Nugget, respectively. The authors suggested that the significantly increased glutathione

content, glutathione reductase, and superoxide dismutase activities of Progress might be a part

of its metabolic resistance to SO2 exposure.

Borland and Lea (1991) investigated the long-term effects of 39, 73, and 100 ìg m-3 SO2

(growing season means) on nitrate reductase, nitrite reductase, glutamine synthetase,

glutamate dehydrogenase, glutathione reductase activity and total glutathione content in

winter barley (Hordeum vulgare L.) cv. Igri. Nitrate reductase activity in tissues harvested in

February, March and April was significantly decreased by 100 ìg m-3 SO2. Nitrite reductase

activity was relatively constant except for significant increases in April (at 100 ìg m-3 SO2) and

May (at 39 ìg m-3 SO2). There was no effect at any concentration of SO2 on glutamine synthetaseor glutathione reductase. Exposure to SO2 significantly increased glutamate dehydrogenase

activity in samples obtained in December, January and June. Total glutathione varied with the

season but there was no accumulation with SO2 exposure. It was concluded that the

concentrations of SO2 were too low to generate a significant response.

Julkunen-Tiitto et al. (1995) studied the effects of SO2 exposure on secondary metabolism

24

(production of phenolics and soluble sugars) in six clones of willow (Salix mysrsinifolia). Clones

were exposed, in fumigation chambers, to 300 ìg m-3 SO2 for 7 h day-1, 5 days week-1, for 3 weeks.

Salicin and chlorogenic acid content were significantly decreased by 15% to over 70%

(depending on clone) while there was no significant effect on salicortin, 2’-O-acetylsalicortin,

(+)-catechin and two unknown phenolics. Since SO2 exposure did not affect salicortin and

2’-O-acetylsalicortin (key molecules in the defense chemistry), it was concluded that willow

resistance to herbivory and microorganism attack was not reduced. Glucose, fructose and

sucrose contents were not significantly affected.

Bernardi et al. (2001) studied levels of soluble leaf proteins and the response of the

superoxide dismutase (SOD) complex of bean plants (Phaseolus vulgaris L.) cv. Groffy after

exposure to SO2 (79, 157 or 236 ìg m-3) for 2, 4, or 7 days. Newly synthesized polypeptides were

detected in all treatments and there were quantitative differences between the control and

treated plants for 6 other protein subunits. The authors indicated that the observed changes in

protein synthesis might be linked to a SO2 resistance mechanism. In addition, SO2 exposure

induced the activation of an additional SOD isoform, which when tested exhibited thecharacteristics of an iron superoxide dismutase (FeSOD). It was concluded that the increased

activity of the FeSOD represented the initial activation of the antioxidant system in response to

radical formation due to oxidation of SO2.

Proline has been shown to protect plants against free radical induced damage. Proline

accumulation is linked to quenching of single oxygen (Matysik et al., 2002). Increase in proline

content as result of SO2 pollution has been observed in maize (Jeyakumar et al., 2003).

Lang et al. (2007) observed that sulphur dioxide after conversion to sulphite in aqueous

solution, becomes a strong nucleophilic agent that attacks numerous compounds in the cell.

Therefore, plants have developed a mechanism to control sulphite levels. They have cloned and

characterized the enzyme sulphite oxidase (SO) from Arabidopsis thaliana which is essential

for detoxifying excessive amounts of sulphite in the cell which is important for the survival of

the plant. T-DNA-tagged A. thaliana plants lacking the enzyme showed a decrease in vitality

during SO2 fumigation and a change in their S-metabolites. The same was found with

RNA-interference (RNAi) plants that were generated for tobacco. On the contrary,

over-expression of SO helped the plant to survive. SO concentrations that are detrimental for

non-transformed wild-type (WT) plants, as was shown with poplar plants which are known to be

particularly sensitive to SO2. Fumigation induced the expression of the enzyme as

demonstrated by promoter-reporter gene fusion, by immunoblot analysis of SO-protein and by

induction of enzyme activity. This implies that SO, as an otherwise constitutively expressed

protein, is under additional control of SO2 in the environment. Similar result was observed by

Brychkova et al. (2007) in tomato and Arabidopsis.

Kim et al. (2007) studied the fuction of secretory class III plant peroxidase (POD, EC

1.11.1.7) in sweet potato (Ipomoea batatas) in diverse physiological processes, including

responses to various environmental stresses. To understand the function of each POD in terms

of air pollutants, changes in POD activity and expression of 10 POD genes isolated from cell

cultures of sweet potato were investigated in the leaves of sweet potato after treatment with

sulfur dioxide (SO2 500ppb, 8h/day for 5 days), ozone (O3 200ppb, 8h/day for 6 days). All

treatments significantly reduced the PSII photosynthetic efficiency (F(v)/F(m)). POD-specific

Physiological & Biochemical Effects of Sulphur Dioxide 25

activities (units/mg protein) were increased in leaves treated with SO2 and O3 by 5.2- and

7.1-fold, respectively, compared to control leaves. As determined by RT-PCR analysis, 10 POD

genes showed differential expression patterns upon treatment with air pollutants and UV

radiation. Among the POD genes, swpa1, swpa2, and swpa4 were strongly induced following

each of the treatments. Interestingly, basic POD genes (swpb1, swpb2, and swpb3) were highly

expressed following SO2 treatment only, whereas neutral swpn1 was highly induced following

O3 treatment only. These results indicated that some specific POD isoenzymes might be

specifically involved in the defense mechanism against oxidative stress induced by air

pollutants in sweet potato plants.

Rai et al. (2007) studied the effects of ambient gaseous air pollution on wheat (Triticum

aestivum L. var. HUW-234) growing in a suburban area where mean concentrations of SO2, NO2

and O3 were 8.4, 39.9 and 40.1 ppb. They observed that lipid peroxidation, proline, total phenol

and ascorbic acid contents and peroxidase activity were higher in plants grown in non-filtered

chambers as compared to filtered chambers.

Rai and Agrawal (2008) assessed superoxide dismutase (SOD) and peroxidase (POD)

activities, ascorbic acid, total phenolics and protein contents at different developmental stages

in two cultivars of rice (Oryza sativa L. cv. Saurabh 950 and NDR 97) exposed to air pollution.

Twelve hour monitoring of ambient concentrations of SO2, NO2 and O3 in filtered chambers

(FCs), non-filtered chambers (NFCs) and open plots (OPs) and observed that lipid peroxidation,

SOD and POD activities, ascorbic acid and total phenolics were higher, whereas contents of

protein were lower in plants of NFCs as compared to FCs.

Sharma and Tripathi (2008) observed significant increase in ascorbic acid in Ficus

benghalensis L. and Dalbergia sisso Roxb. under influence of ambient sulphur dioxide, nitrogen

dioxide, suspended particulate matter (SPM), respirable suspended particulate matter (RSPM),

dust-fall rate (DFR).

Al Sayegh Petkovsek et al. (2008) observed the increased amount of ascorbic acid (vitamin C)

and alpha-tocopherol (vitamin E) in needles of Norway spruce (Picea abies L.) in the area

influenced by sulphur emissions from the Sostanj Thermal Power Plant (STPP), Slovenia.

26

IntroductionSulphur dioxide affects a number of plant

processes in a variety of ways. Sulphur dioxide gasdissolves in extra cellular fluid of plants and reacts with plant materials to produce ionic species and freeradicals, which are generally more reactive thansulphur dioxide (Hoffman and Jacob, 1984). Thisdissolved sulphur dioxide is potentially capable ofbehaving as an oxidant and reductant depending uponredox potential of the system. As a result of reaction ofthese ionic species with lipid and proteins in cell wallsand membranes, chain reactions are initiated andgiving rise to more free radicals such as superoxides,single oxygen, hydroxyl ion (OH-) etc. So, the level ofascorbic acid, b-carotene and phenolic compoundsincrease which provide protection against sulphurdioxide phytotoxicity by removing these free radicals(Mandal and Mukharji, 1998; Jeyakumar et al., 2003). In addition sulphur dioxide phytotoxicity is due to sulphite ions, which get incorporated in cell water content andreduces the cell sap pH. These sulphite radicals damagethe photosynthetic membrane and acidic condition alsoinduces the photosynthetic inhibition and reduces theplant growth (Wellburn, 1982). Bleaching of pigments isan oxidation process and sulphur dioxide is partlyresponsible, since light is also responsible. Sulphurdioxide is responsible for making the photoxidation ofchlorophyll molecules irreversible, resulting in anirreversible injury (Nieboer et al., 1976).

AMELIORATION OF SULPHUR DIOXIDE

PHYTOTOXICITY

6

@ Introduction

@ Amelioration of SO2 Phytotoxicity

Chapter Content

Amelioration of Sulphur Dioxide Phytotoxicity 27

Amelioration of SO2 PhytotoxicityCowling and Lockyer (1978) studied that how nutrient supply influences the effect of SO2 onperennial ryegrass. They exposed plants for 85 days, in chambers, to a daily average of 55 ìg m-3

SO2 or filtered air. Plants were grown with or without added soil sulphur and two rates of addednitrogen (N: low and high). Plants grown with high N and no added soil S developed S deficiencysymptoms. The S deficiency symptoms were reduced in the high N treatment in the presence ofSO2 while shoot dry weight was more than doubled and root dry weight was almost doubled.When high N plants were supplied with soil sulphate, the addition of SO2 to the atmosphere didnot alter root or shoot dry weight. The number of tillers increased with increased N, with addedsoil sulphate, and when exposed to SO2. There was little difference in shoot or root dry weightsand number of tillers in the low N treatments in the presence or absence of SO2. Total shootsulphur and sulphate-S generally increased with the addition of soil sulphate and exposure toSO2; although, high N treatments had lower levels of both, which was attributed to dilution, asthe high N plants were larger.

SO2 gas mainly diffuses in leaves through stomata. So, antitranspirants may help against air pollution by covering the stomatal apertures. It has been suggested that the foliarapplication of chemicals such as OED (oxyethylenedecosanol) green may be used to protectplants near stationary source of SO2 emission. Perhaps OED green and other antitranspirantsform a thin film over the leaves and may reduce injury caused by sulphur dioxide pollution,however, the efficacy of antitranspirants in preventing sulphur dioxide damage is uncertain,since they are also likely to affect the normal diffusion of carbon dioxide. Moreover, applicationof antitranspirants on large scale to protect plant from pollution may create its own problem(Varshney and Garg, 1979).

Shimazaki et al. (1980) observed that chlorophyll breakdown in SO2 exposed plants canbe checked by using various free radical scavengers. Winterhalden, (1981) reported that Ca++ asmineral nutrient provides protection to SO2 exposed plants. Nandi et al. (1981) reported thatpotassium ascorbate acts as antidote to SO2 phytotoxicity. Nandi et al. (1984) observed calciumhydroxide spray checks chlorophyll degradation by neutralizing the acidity of SO2 in plants.

Rao et al. (1985) sprayed aqueous solution of lime water and sodium benzoate onSO2-exposed Vigna sinensis plants and observed lower degradation of photosynthetic pigmentsand better growth than SO2-exposed plants. Singh and Rao (1985) reported amelioration ofSO2-induced injury through foliar spray of urea.

Krishnayya and Date (1996) studied the impact of SO2 and SO2 + ascorbic acid on growthand partitioning of dry matter in Trigonella foenum-graecum L., two-week-old plants wereexposed to SO2 for 2 h daily over a 42 day period. One of the exposed sets was treated withascorbic acid. Although ascorbic acid treatment could mitigate the effect of SO2, the differenceswere not found to be statistically significant. Significant changes were seen in fruit yield,suggesting that the effect of ascorbic acid is cumulative.

Agrawal and Verma (1997) investigated whether varying the levels of nitrogen (N),potassium (K), and phosphorous (P) in the growth medium would affect the response of wheat(Triticum aestivum L.) cvs. Malviya 206 and Malviya 234 to SO2. Wheat was grown in the fieldwith 6 nutrient treatments applied after a basal nutrient addition. Treatments were: noadditional nutrients, a recommended application rate and 4 combinations of N, P, and K. Thirtydays after sowing, plants were exposed in open-top chambers to 390 ± 20 ìg m-3 SO2 for 4 h day-1,5 days week-1, for 8 weeks. Unfertilized plants exposed to SO2 had the greatest dry weight,height, and yield reductions while plants grown with recommended or 2 times the recommended levels of NPK were able to alleviate SO2 effects to the greatest extent. They concluded that bothnutrient deficiency and SO2 caused the observed reductions of measured parameters but thatthe addition of NPK in different combinations was able to ameliorate the adverse effects of SO2.

Effects of SO2 Pollution on Plants and Its Amelioration28

Bhagya Lakshmi and Raza (2000) report the nitrogen and sulphur levels of 11 tropicaltrees growing under industrial establishments and experimental results on ameliorating SO2 in tree sampling by nitrogen fertilization. They analyzed percentage injury due to SO2 and itspercentage recovery due to nitrogen fertilization at weekly intervals and observed that nitrogenfertilization is quite useful in reducing the SO2 toxicity.

Deepak and Agrawal (2001) grew two cultivars (PK472 and Bragg) of soybean (Glycinemax L. Merr.) in open-top chambers maintained at atmospheric CO2 concentrations of 350 and600 ppm alone and in combination with 60 ppb sulfur dioxide (SO2). Exposure to elevated SO2

significantly reduced every growth parameter studied; total plant biomass and grain yield werereduced by approximately 18% in both cultivars. In contrast, elevated CO2 by itself significantly increased every growth parameter in both cultivars, boosting total plant biomass and grainyield by averages of 30 and 34%, respectively. Moreover, when the plants were exposedsimultaneously to elevated CO2 and SO2, the negative effects of SO2 were completelyameliorated.

Han (2001) observed the relation between tree stomatal infiltration and SO2 injury andthe protection effect of ABA. The effects of SO2 smoking to the selected trees were observed andthe results show that stomatal infiltration was a comparably constant index for certain treespecies. The index is also positively correlated with K+ efflux in leaf(r = 0.92, alpha < 0.01). Inthe experiment of SO2 smoking, the effect on infiltration of same species under different SO2

concentration was little, less than one grade, while K+ efflux increased with the increment ofSO2 amount absorbed by the leaves. When the leaves were sprayed with ABA solution, thehigher the ABA solution concentration was, the lower the K+ efflux was. He concluded that theABA solution on leaves has remarkable effect of protection of SO2 injury.

Tomato (Lycopersicum esculentum) fruits contain many antioxidants such as lycopene,vitamin C (ascorbate), vitamin E (tocopherol), polyphenols such as kemferol, querceten andhuge levels of total phenolics typically has high oxygen radical absorbance capacity (ORAC)value, which helps in amelioration of SO2 phytotoxicity (Singh et al., 2004).

Singh et al. (2005) observed that increased fertilizer application over recommended dose of

N, P and K resulted in positive response by reducing losses in photosynthetic pigments and total

biomass by ambient air pollution of Allahabad city.

Agrawal, M. and Singh, J. (2000). Impact of coal power plant emission on the foliar elementalconcentrations in plants in a low rainfall tropical region. Environ. Monit. Assess., 60: 261-282.

Agrawal, M. and Verma, M. (1997). Amelioration of sulphur dioxide phytotoxicity in wheatcultivars by modifying NPK nutrients. J. Environ. Manag., 49: 231-244.

Agrawal, M., Nandi, P. K. and Rao, D. N. (1985). Effects of sulphur dioxide fumigation onsoil system and growth behaviour of Vicia faba plants. Plant and Soil, 86: 69-78.

Agrawal, M., Singh, B., Rajput, M., Marshall F. and Bell, J. N. (2003). Effect of airpollution on peri-urban agriculture: a case study. Environ. Pollut., 126 (3): 323-329.

Agrawal, S., Singh, R. and Sahi, A. (1995). Cytogenetic effect of sulphur dioxide on cytotypesof Solanum nigrum complex. Cytobios., 83: 41-47.

Agrawal, M., Nandi, P. K. and Rao, D. N. (1982). Effect of ozone and sulphur dioxidepollutants separetly and in mixture on chlorophyll and carotenoid pigments of Oryza sativa.Water Air Soil Pollut., 18: 449-459.

Agrawal, M., Nandi, P. K. and Rao, D. N. (1983). Ecophysiological responses of egg plants toozone, sulphur dioxide and mixture of these two pollutants. Indian J. Air Pollt., 4: 27-32.

Agrawal, S. B. and Madhoolika (1991). Effect of sulphur dioxide exposure on chlorophyllcontent and nitrogenase activity if Vicia faba L. plants. Bulletin of Environ. Contam. AndToxicol., 471(5): 770-774.

Al-Qurainy, F. H. (2008). Effect of air pollution and ethylene diurea on broad bean plantsgrown at two localities in KSA. Int. J. Bot., 4(1): 117-122.

Al-Sayegh Petkovsek, S., Batic, F., Ribaric Lasnik, C. (2008). Norway spruce needles asbioindicator of air pollution in the area of influence of the Sostanj Thermal Power Plant,Slovenia. Environ Pollut., 151(2): 287-91.

Amer, S. M., Mikhael, E., El-Ashry, Z. M. (1989). Cytogenetic effect of sulphur dioxide onVicia faba plant. I. Cytologia., 54: 211-221.

Arnon, D. I. (1949). Copper enzymes in isolate chloroplasts, polyphenol oxidase in Betavulgaris. Plant Physiol., 24 : 1-15.

Arora, A., Byrem, T. M., Nair, M. G. and Strasburg, G. M. (2000). Modulation of liposomalmembrane fluidity by flavonoids and isoflavonoids. Archives of Biochemistry and Biophysics,373: 102-109.

Ashenden, T. W. and Mansfield, T. A., (1977). Influence of wind speed on the sensitivity ofryegrass to SO2. J. Exp. Bot., 28: 729-735.

Ashenden, T. W., Hunt, R., Bell, S. A., Williams, T. G., Mann, A., Booth, R. E. andPoorter, L. (1996). Response to SO2 pollution in 41 British herbaceous species. Funct. Ecol., 10: 483-490.

Bates, L. S., Waldren, R .P. and Teare, I. D. (1973). Rapid determination of free proline forwater-stress studies. Plant & Soil, 39: 205-207.

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