botany topics

BOTANY TOPICS

B 6 GROWTH AND GROWTH REGULATOR IN PLANTS

1. Introduction

2. Scientist

3. Glossary

4. Growth

i. Definition

ii. Region of growth

iii. Phases of growth

iv. Growth curve

5. Growth regulator

i. Defination

ii. Role of the following plant hormones

1. Growth promoter : Auxins

Gibberllins

Cytokinins

iii. Synthetic Growth regulators and their application : with reference to IAA, IBA, NAA 2,4- D, BAP and Ethephon

6. Question BankOne Marks QuestionsTwo Marks Questions

Five Marks Question

7. Model Answers

INTRODUCTIONGrowth may be considered as one of the basic attributes of all living organisms, and plants in particular are of special significance because these continue to grow throught their life.

Growth is basically a biological phenomenon which is accomplished by various physiological processes involving synthesis and assimilation of new protoplasmic materials like carbohydrates, proteins, and lipids by living cells. Growth is preliminarily concerned with increase in size, volume or weight of an organismGrowth of organism is internal or intrinsic due to synthesis of new cellular materials, increase in cell size and increase in cell number. This phenomena is called Intussusceptions, where as in non living objects there is increase in back due to deposition of similar materials on outside. This is extrinsic growth and the phenomina is called Accretion.The growth in plants and its different organs is regulated by certain chemicals compounds produced in very small quantities. These specific chemical substances are termed plant hormones or phytohormones (growth regulators). Plant hormones are synthesized with in the plant cells of growing parts in young leaves, terminal buds or shoot apex and usually translocated downward through the phloem tissues.Growth hormones or growth regulators are considered as Chemical messengers which sometimes inhibit growth of plant organ.

1. 1906 Starling : Used the term hormone for the first time for stimulating substance.

2. 1948 Thimann : Used the term phytohormones for hormones of plants.

3. 1880 Charles Darwin and his son Francis : Worked on canary grass (Phalaris canaries) and discovered the existance of some growth promoting substance.

4. 1914 Boysen Jensen : Used Oat (Avena sativa) seedling to demonstrate the presence of auxins at the stem tips.5. 1928 Went: Provided final proof of presence of auxin through experiments on Oat.

6. 1934 Kogl et al : Isolated three types of auxins and studied their chemical structure.7. 1933 Thimann and Skoog : Found that on removal of apical buds, the axillary buds begin to sprought and a large number of branches are formed.8. 1926 Kurosawa ( A Japanese Plant Pathologist) : Discovered Gibberellins in fungus Gibberella fujikuroi, while working on rice seedlings with foolish growth as Bakane disease.9. 1938 Yabuta and Sumiki : Extracted chemical from the fungus, which is responsible for elongation of seedlings and called it Gibberellin.10. 1963 Letham : Proposed the term cytokinin for true cell division factors present in plants.11. 1950 Miller, Skoog and co-workers : Discovery of Cytokinin.12. 1957 Richmond and Lang : Showed the effect of cytokinin in delaying senescence, which is called Richmond Lang effect.13. 1963 Carns and Addicott : Discovered Abscisic Acid while working on cotton.14. 1969 Pratt and Goesch : First recoginised the ethylene as a natural plant growth regulator.

GLOSSARY

1. Sigmoid curve : The growth rate of a plant against the time plotted on a graph pape gives a S-shaped curve called Sigmoid curve or Growth curve.2. Grand period of Growth : The total period of time during which all the phases occur.3. Coleoplile : In grasses, oats, maize etc, the plumule in the seed remains covered by a protective cap like structure called Coleoptile.4. Hetero auxin : Auxin isolated from human urine.5. Anti auxins : Substances inhibiting polar transport of auxins.6. Polar Transport : Basipetal movement of auxins from stem apex and acropetal movement from root to the shoot through living cells.7. Abscision : It is phenomenon of a plant which includes unorganized shedding of its organs such as leaves, petals, of flowers and ripe fruit.8. Parthenocrapy : Formation of fruits without fertilization.9. Bolting : Stimulation of rapid stem elongation and conversion of that in floral axis bearing floral primordial.

10. Senescence : The aging process of leaves is usually accoumpanied with loss of chlorophyll (i.e yellowing) rapid breakdown of protienes is called senescence.11. Ethrel Ethephon : Chloroethyl phosphoric acid.12. TIBA Triodobenzoic Acid13. NTA : Naphthyl thalamic acid14. IAA : Indole Acitic Acid15. ABA : Abscisic Acid16. IBA : Indole Butyric Acid17. 2, 4-D : 2 4 Dichlorophenoxy Acetic Acid or 2, 4,5-T :2,4,5- Tetracholoro phenoxyacetic acid18. BAP : Benzyl Amino Purine19. NAA : Napthalene Acetic Acid20. Richmond Lang effect : Effect of cytokinin in delaying the senescence of leaves.

21. Dormin : Earlier ABA was known as dormin due to its ability to promote abscission in plant organs.

22. Ethrel : Trade name Ethephon23. SDPs : Short day Plants24. LDPs : Long day plants

GROWTHDefination:

Growth can be defined as a permenant and irreversible increase in the size of a cell organ or whole organism usually accoumpanied by an increase in dry weight.

F.F. Blackmann defines growth as,

Finished product of the successful metabolic loom.

Region of growth in Plants:

The stem tips and root tips in plants show 3 distinct region of growth.

They are as follows:

1) Region of cell division.

2) Region of cell elongation.

3) Region of cell maturation.

Region of cell division or cell formation:

At the extreme tips of stems and roots there is a group of small cells, which continuously show division. The cells show mitosis and results in the formation of daughter cells. This region where cell divide is called region of cell formationRegion of cell elongation : The derived cells show linear enlargement due to action of growth harmones and that results in the elongation of stems and roots. The region where the cell elongates is called region of cell elongation.

Region of cell maturation : The cells which are enlarged enter into the third region of growth whrer cells differentiate into permenant tissue, is called the region of cell maturation,Based on duration, plants show two types of growth:

a) Limited Growth : A structure grows to a certain size and stops growing furthers e.g. leaves flowers etcb) Unliited or Indeterminate growth : Structure continue to grow indifinetaly and for years together.E.g: Stems, leaves, monocot leaves, algae and fungi

Phases of Growth : Growth in plants takes place through 3 phases.

1) Phase of cell division or phase of cell formation

2) Phase of cell enlargement or phase of cell elongation

3) Phase of cell maturation or differentiation phase

Phase of cell division or cell formation phase :

This is a phase in which meristematic cells divide frequently and regularly by mitosis, while some of the daughter rcells remain meristematic as initials, others enter the next phase of growth.

Phase of cell enlargement or elongation :

The cells formed during cell division show linear enlargement due to the action of growth hormones and that results in elongation of stems and roots. The cells increase in size mainly due to vacuolation. A big central vacuole appears which puhes cytoplasm as a thin layer against cell wall. The new cell wall material is synthesized to cope with the enlargement.

Phases of cell maturation and differentiation :

The cell differentiation involve several different anatomical and psychological specialization

For example : The cells which are designed to becom vascular elements such as sieve elements and xylem elements generally mature in to greatly elongate elements and these participate in translocation of water, solutes and organic food. The root hair cells are specialized for absorbing water, while cholorophyllus cells of the leaves performe the function of photosynthesis.

This is the phase where the enlarged cells differentiate into permentant tissue.

Growth Curve (sigmoid curve) :

The growth rate of plant against the time plotted on a graph gives a S-shaped curve called Sigmoid curve or Growth curve.

It is observed that the rate of growth not uniform and an analysis of growth curve reveals that the growth accours in 3 distinct rate as follows.

1. Lag Phase of growth : Growth starts at a slow rate known as lag phase of growth. It is a early period of slow growth

2. Long phase (Exponenttial phase) of growth : The lag period is followed by a rapid groeth called log phase of growth. It is a middle period of slow growth.

3. Final phase of Slow growth: The long period is followed by a decreasing growth rate.

Finally the growth comes to halt which is known as steadily state.

Grand Period of Growth :

The total time during the course of growth constitutes grand period of growth.

Grand Period Curve:

The S shaped curve is also know as Grand Period Curve.

Reproductive Growth :

Reproductive growth is characterized by the formation of flower.

Floral evocation :

The events accouring in the shoot apex structure are togrther called evocation.

In several plants flowers appear to be under control od daily length of light or photoperiod and temperature.

Photoperiodism :

It is ability to detect day length or to perceive the light stimulus.

Photoperiod:

Day length was the determining factor in flowering. This phenomina is called as Photoperiod. Flowering plants are classified into the following groups based on their flowering response to photoperiod.

a) Short day plants (SDPs): These prodyce flowers on when the day length is shortest than the cerain period. E.g.: tobacco, soyabene, chrysanthemum, strawberry etc.

b) Long day plants (LDPs) :These produce flowers only when the day length hours are longer than certain critical period E.g: Spinach, Cabbage etc.

c) Day neutral Plants:These plants produce flowers over a wide range of photoperiod and hence flowering is not regulated by day length.

e.g: tomato, chilli, 4 O clock, maize.

Vernalization:

If flowering will take place only when seeds or plants have been subjected to low temperature say 0 4 C for a few - weeks . This is called vernalization.

Dormacy :

When photoperiod and temperature is not favorable for active growth, many plants undergo period of inactivity. This is called dormancy. Activity starts again when eternal conditions become favorable.

GROWTH REGULATORSThe different metabolic activities in plants are controlled by different growth regulators or plant hormones. They are also called phytohormones.

Defination:

A plant hormone is defined as Organic substance produced naturally in higher plants, controlling growth or other psychological funcrions at a site remote from its place of prodyction and active in minute amounts.

Phillips defined growth hormones as

Substance which are synthesized in particular cell which are transported to other cells, where in extremely small quantities influence development processes.

Types of phytohormones (Plant Hormones) :

Basically plant hormones are chemical regulators, which control the psychology of growth. Based on nature of control or regulation of plant hormones are classified in to 2 groups.Namely : a) Growth promoting hormones.

b) Growth inhibiting hormones.

There can be yet another way of classifying as

a) Natural growth substances : These are synthesized in plants.

b) Synthetic growth substances : These are synthesized artificially in laboratories.

Natural growth regulators:

A.Growth promoters: These hormones promote the plants growth. There are mainly three types.

1) Auxins

2) Gibberellins

3) Cytokinins

B. Growth inhibitors: Which inhibit the growth. 1) Abscisic acid and 2) Ethylene

A) Growth Promoters :1)AUXINS:The term auxins includes all those chemicals substances which promote growth of stem.

The principle naturally accouring auxin is IAA ( Indole 3 Acetic Acid) Discovery :

The pioneering work in the field of hormonal study was done by Charles Darwin and his son Frances Darwin, on the canary grass (Phalaris canariensis).Boysen-Jensen (1914) used oat (Avena sativa) seedlings to demonstrate the presence of auxins at the stem tips.

F.A. went and F.W. Went conformed that the coloeoptile tips of oat synthesized certain chemical which migrated downward and caused the longitudinal growth one side, the named this substance as auxin and concluded that no growth can acccor without auxin This experiment is popularly called as Avena curvature Test.

Types of Auxins: Three types of ausxins are and isolated and studied by Kogl et al. Those are

1) auxin- a from human urine.

2) Auxin- b from corn germ oil

3) Heteroauxin (IAA) from human urine.

IAA has been detected in all higher plants.

Derivatives of IAA : Derivatives of IAA have been deteced from various plants. They are Indole- 3- aceticacid, Indole- 3- Butyric acid and Indole -3-ethanol.

Occurrence : The auxins are found in higher amount interactively growing regions. In general ausins are located mainly in young and actively growing regions, such as shoot apex, root apex, lateral meristims and enlarging leaves.

Polar transport : The auxin generally involve from sem apex downward to base (i.e basipetal) and from root upward to shoot through living cells. Such a movement of auxinis know as polar transport.Antiauxins : Polar transport of auxin is inhabited by 3 antiauxins thay are:

1). TIBA Triiodobenzoic acid

2). NTA Naphthyl- thalamic acid

3). Ethylene cholorhydrin

Psychological role of Auxins (Functions):

Some of the important functions of auxins are as follows.

1) Apical dominance : The auxins present at the tips dominates over the auxillart buds and make them remain dormant.

Thimann and Skoog found that on removal of apical buds, the auxillary buds begin to sprout and a large number of brancehes are formed,

This principle is used in pruning of plants and preservation of potato tubes2) Cell elongation : Auxins stimulate cell elelongation in stems and coleoptiles. The cell elongation and enlargement are brought about by several mechanism.

For e.g.: Cell elongation and enlargement can be observed in phototropic curvature where ubilateral light unequacy distribustes the organ in stem. The higher the concentration of auxin on the shaded side causes the cells on that side to divide and elongate more rapidly resulting in curvature odf stem tip towards unilateral light.

3) Cell differentiation : Auxins help in cell differentiation, especially of vessels elements and fibers of xylem.

4) Abscission : Natural auxins in plants prevent the abscission of leaves, fruits, flowers etc.

5) Tissue Culture : In tissue culture the growth of callus requires the presence of auxins. It increases the cell division in the area of injury.

6) Healing : The healing hormone traumatic acid and trauation is actually auxin. It increases cell division in the area of injury.

7) Nodule Formation : Nodule formation in legumes occur in response to increase formation of auxin.

8) Shoot and root growth : Auxins promote the growth of shoot at a retavely higher concerns and that of root at a relatively lower concern.

9) Root Initiation : Lower concentration of auxin at the root tip initiate and promote development of normal roots, where as higher concerns of auxin inhibit the elongation of root but promote number of lateral roots.

10) Parthenocrapy : Auxins induce the formation of parthenocarpic fruits.

Natural parthenocrapy occurs in plants like banana and grapes due to higher concentration of quxins in the ovaries before fertilization.11) Xylem differentiation : Auxin promote xylem element differentiation. This property is used in bud grafting.

COMMERCIAL USES OF AUXINS:

a) Rooting of cuttings: Auxin treatment stimulates rooting of cutting in most plants. IBA is known as rootone because of it. Another common auxin used for rooting is NAAb) Weedicides and Herbicides : In higher concentration many synthetic auxins are used as Weedicides and Herbicides. Ex/; 2, 4-D are commonly used in killing broad leaved weeds in cereal crops.

c) Parthenocarpy : Seedless fruits are raised by spraying unpolliniated flowers with dilute solutions of IAA and IBA

d) Preharvest fruit drop : Premature is prevented by application of 2, 4-D (Ex:Apple,Orange) and NAA (Ex:Tomato)

e) Flowering : Plants which are difficult to flower can be made to do so by spraying them with 2,4- D and NAA.(Ex: Litchi,Pineapple)

f) Frost Resistance: Damage due to frost is reduced by application of sodium salt of NAA

g) Higher Yield: In apple, flowers are born only on dwarf shoots. NAA increases the number of dwarf shoots. Therefore, more flowers and fruits are born on the plants.h) Sweetening of Fruits : Application of auxin like IBA increase sweetness of many fruits

2) GIBBERELINS :

Gibberellins are weak acidic plant hormones which peomote the growth of certain plant organsDiscovery : Gibberellins were discovered by Japanese plant pathologist Kucosawa.

While working in the rice fields, Kucosawa observed growth of fungus Gibberella fujikuroi; (Fusarium spacies) on tall plants of rice. He called his growth of rice seedlings as Bakane disease.

Yabuta and Sumiki demonstrated that the fungus secretes certain chemicals, responsible for elongation of seedlings. They called the extraction as Gibberelin Gibberelllic acid (GA)

Types of Gibberellins :Many different types of Gibberellins were discovered and are named as GA1, GA2, GA3, GA4,----------

Psychological role or functions of Gibberellins :

1. Elongation of stem : When Gibberellins are sprayed over genetically dwarf plants, it induces stem elongation e.g: Spray of Gibberellins over dwarf pea, dwarf maize etc help to overcome genetic dwarfism2. Bolting and flowering : Plants with rosette of leaves attached to the short axis (e.g: Sugar beet) when sprayed with Gibberellin, shows excessive elongation of axis and starts flowering.The stimulation of rapid cell elongation and conversion of that into floral axis bearing flower primordial is called bolting.

3. Production of parthenocarpic fruits : Gibberellins are more effective than auxins in production of parthenocarpic fruits.

E.g: Tomato, cucumber, and certain varieties of grapes.

4. Breaking dormancy : Spray of Gibberellin breaks dormancy of seeds, buds and underground organs. E.g: bulb, tubes, corn etc.

5. Substuting the cold treatment : A spray of gibberlin in proper concentration over biennials substitutes the cold treatment and are made flowe in one year.

6. Flowering in a long day plants : In long day plants Gibberellins can replace the long day requirement and promote flowering even under long inductive photoperiod.

(Dormancy : Natural breaking of dormancy )

7. Growth of Aerial parts : Cell growth of stem, leaves and other aerial parts is controlled by Gibberellins along auxins

8. Maturity : Transition from juvrnile stage to mature stage is regulated by gibberlins.

9. Seed germination : Gibberellins counteract inhibitors and induce synthesis of various types of hydrochloric enzymes for mobilization of reserve food.10. Vernalization : Gibberellins can replace the requirement of low temperature.

E.g.: Chrysanthemum

Commercial use of Gibberellins :

a) Parthenocarpy : Gibberellins are most effective in inducing development of seedless fruits or parthenocrapy in pomes (Ex: Apple). In tomato Gibberellin is 500 times more effective than auxinb) Fruit Growth : Spraying Gibberellin over pollinated flowers and younfg fruits increae the number and size of the fruits. Ex: Grape Tomatoc) Flowering: Gibberellin treatment is used in inducing off season flowering in long day plants and plants requiring cold climated) Breaking Dormancy: Dormancy of buds, seeds, and underground structures can be broken by the application of Gibberelline) Delayed Ripining : Application of Gibberellin delays the ripining of citrus fruits. Such fruits can be stored for long period.f) Malt : Germinating barely grains produce more malt when provided with Gibberellins.g) Sugarcane : Sugarcane yield more sugar when sprayed with Gibberellin because when it is provided with the Gibberellin there will be increase in internodal length as well as higher sugar storage.3) CYTOKININS :

Cytokinins includes those phytohormones which stimulate and help in cell division and cytokinesis.

The term Cytokinins was proposed by Letham

Discovery : Cytokinins were discovered by Skoog Miller and their co workers.

Cytokinins are degradation product of adenine, a compound of nucleic acids and ATP. Cytokinins has been obtained for coconut milk yiest etracts, apple extracts etc.

Chemically Cytokinins is 6 furfuryl amino prine.

Physiological role of Cytokinins:Important roles or functions of Cytokinins are as follows.

1. Cell division : Cytokinins induce cell division in the non meristematic tissue.2. Cell enlargement : Cytokinins induce cell enlargement also3. Morphogenisis : Cytokinins also has the ability to cause morphogenetic changes in an undifferentiated cells Skoog and Miller (1950) did the tobacco pith culture in a medium containing equal concentration of auxine and cytokinins. They showed that the cell in the path showed active cells division and developed in to the callus. When they increased concentration of cyrokinins the callus developed the bud, which later developed into microshoot.

The positive effect of cytokinin on regeneration of shoots from cultured stem, root and leaf explants has been reported in many plants.

4. Counteraction of Apical dominance : Cytokinins counteract or neutralize the effect of auxin on apical dominance. Wickson and Thimann (19580 in one of their experiment concluded that the apical dominance might be under control of a balance of concern between endogrnous Cytokinins and IAA

.

5. Delay of senescence, Richmond Lang effect : The ageing process of the leaves usually accoumpanies with loss of chlorophyll (i.e yellowing) and rapid breakdown of protienes. This is called senescence.

Richmond and Lang showed that this senescence could be postponed to several days in detached Xanthium leaves by Cytokinins treatment. This effect of Cytokinins in delaying the senescence is called Richmond Lang effect of growth inhibitors.

Commercial use of Cytokinins :a) Cut flowers : Cut flowers can be made to remain for several days if they are treated with Cytokinin solutionb) Shelf lifr ; Shel life of fruits and vegetables can be prolong by many weeks if they are treated with cytokinin solution.c) Resistance : Plants treated with Cytokinin develop a hardness to cold, frost heat and pathogrns.d) Senescence : Cytokinin delays the development of senescence in intact leaves and other plant parts.e) Tissue culture : Cytokinin is essentially a in tissue culture as it is required for both cell division and morphogrnisis In amny tissue culture coconut milk, yeast extracts, or apple fruit extracts provide the necessary Cytokininf) Pomalin : A combination of synthetic Cytokinin , GA and GA is commercially called Pomalin It is used for increasing the fruit size (Ex:Apple).B. GROWTH INHIBITOR:In addition to growth promoters, or hormones, many plants also produced growth inhibitor which inhibit growth.

1) ABSCISICACID (ABA or Abscission)

Discovery : ABA was discobered by Carns and Addicott (1963) while working on the physiological studies of shedding cotton balls and leaves.

Earlier ABA was know as dormin. ABA is so called because of its ability to promote abscission of leaves, fruits, seeds, embriyo etc. It is produced in all parts of plants.

Psychological role of ABA (Function of ABA):

1. It promots abscission of leaves, flowers and fruits. It includes abscission layer in the petiole and pedicel and results in their abscission.

2. It prevents the elongation of shoot keeps the embryos and buds and dormant,

3. ABA takes part in the stomatal regions, where there is drought the plants produce more ABA and induce closure of stomata.

4. It acts as a stress hormone in plants when there is shortage of water, salinity, chilling, and freezing temperature.

5. It promotes senescences of leaves

6. ABA found to decrease RNA and protiene synthesis in leaves.

7. It inhibits development of embriyo in seeds.

8. Inhibits cell division and cell elongation

Commercial use of Abscisic Acid

a) Dormancy : It can be prolong dormancy of buds, seeds and storage organs.b) Rooting : Abscisic acid is useful in promoting rooting of stem cutting of some plants. Ex: Bean, Ivy

c) Flowering : It can induce flowering in short day plants grown under long day condition Ex:Black-currant, Straw-berry

d) Antitranspirant : Fine spray of Abscisic acid over the leaves reduce transpiration due to its effect on partial closure of stomata. Gaseous exchange is not much affected . The effect on transpiration and photosynthesis is 56:14%

e) Control growth : Abscisic acid keeps growth under check by counter acting the effect of growth promoting hormones, especially gibberlin. Because of it ABA is also called antigibberellic hormone. ABA not only checks seed germination and growth of excised embryos, but also general growth including multiplication and growth of duck weed.

2.ETHYLENE :

It is gaseous plant hormone. It is a product of metabolism of the amino acid methionine and produced in nodes of stems, ripening fruits and senescing tissues.

Discovery : It was Pratt and Goeschl in 1969, first recognized ethylene as a natural plant growth rate regulator. Ethylene production takes place in moist fruits, flowers, leaves of certain plants and certain fungi

Psychological effect of Ethylene :

1. It induces flowering in pinepapple plants.2. Promoters post harvest ripining og fruits like bananas, apples, pears, tomatoes, citrus fruits, hence ethylene is widely used commercial to induce fruit riprning.3. Induce the formation of root hair in some plants.4. It ascellerates leaf abscission and stimulates the abnormal growth of auxillary buds in some plants5. It accelerates the rate of respiration of potatoes and also inhibits the sprouting of potatoes.6. It promotes senescence.7. Influence budding in onions and stimulates the germination of seeds in some species.8. Spraying of ethylene in young stages reduce the incidence of pests an diseases in crop plants.Commercial use of Ethylene :a) Fruit ripening : Ethylene or ethepon is used in artificial ripening and colour changes in fruits. Ex:: Banana, Apple , Mango It brings about degreening of citrus fruits (ripening is not affected in citrus fruits).b) Synehronisation of Flowering and Fruit set : In pineapple and related plants flowering and fruit set are synchorinised with the help of ethylene.c) Fruit Thining : The hormone is sed in flower and fruit thinning for better growth of remaining ones. Ex: Cherry, Walnut.d) Feminising Effect : Application of Ethylene increases the number of female flowers in cucurbits. This increases the number of fruits.e) Compact Flowering Stem : Ethylene inhibits terminal growth and promotes lateral growth Hence it is used in producing compact flowering stemf) Sprouting of storage organ : Ethylene is used to break dormancy and induce spourting in storage organs like tubers, rhizome, corns, bukbs etc.

C) Synthetic Growth Regulators and their applications :

Synthetic Growth Regulators :

Biochemists studied the structural properties and application of IAA and kinetin and prepared similar compounds in their labouratories. They are the synthetic growth regulators, They are also called artificial growth regulators.

Some examples of synthetic growth regulators are IAA (Indole Acetic Acid), IBA (Indole butyric acid) NAA (Napthalene Acetic Acid) , 2-4D 92-4-Diphenony Acetic Acid), BAP (Benxyl Amino Purine) and Ethepon.Among these IAA, IBA and 2-4D are synthetic auxins. BAP is synthetic cytokinin and Ethephon is a synthetic ethylene- releasing compound.

Practical application of synthetic growth regulators:

Synthetic plant growth regulators (PGR) are used, the rate of application is more critical. Many PGR effective only if applied in a certain stage and some are more effective if applied in the root zone, where uptake can be greater than when the same is sprayed on foliage.

Practical application of some PGR are as follows :

1. IAA (Indole Acetic Acid) : IAA is the common plant growth regulator generally called Auxin. It is widely used because of growth promoting properties.a. Cell dicision in vascular cambium : It is promoted by IAA, resulting in seacondary growth.b. Cell elongation : This promotes the growth and elongation of stem and stimulates the cell walls to streatch.c. Apical Dominance : This phenomina cativates the lateral buds and activates the growth of apical and terminal bud. Tus promotes the growth in length of shoots.d. Application of IAA : in very low concentration promotes the root growth. In higher concentration it inhibits the root growth but it increases the number of branch roots.e. Abscission : Abscission is unorginizrd shedding og plants parts like leaves, unfertilized flowers and fruits.A layer of dead cells called abscission zone is developed by the action of auxins (IAA) at the base of these parts. These layers prevents water supply to these organs causing their premature drop.

2.IBA (Indole Butryic Acid) :It is also a natural growth promoting auxin.

a) It induces cell differentiation

b) It controls apical dominance.

c) It prevents pre harvesting fruit drop

d) It initiates flowering and fruit formation.

e) It inhibits sprouting in potato tubes.

f) It controls excessive lateral root formation

3) NAA( Napthelene Acetic Acid) :

This is also growth promoting auxin, widely used in agriculture and holticulture the following.

a) Flowering in plants like pineapple and litchi by application

b) Development of root in stem cutting

c) Natural fruit setting

d) Prevent potato sprouting

e) Promotes asexual reproduction

4.2,4-D (2,4- Dichlorophenoxy acetic Acid) :

This is also a synthetic auxin with following application

a) It is a powerful and selective weed killer.

It eliminates broad leaved dicot plants without affecting natural monocot . Thus it finds it application as a weedicide in pure crop fields of cerels.

b) Induce flowering in commercial crops like pineapple and litchi.

c) Prevents pre harvesting fruits drops (abscission)

It inhibits sprouting of potatoes.

5.BAP(6,Benzyl Amino Purine) :

It is a cytokinin (or kinetin) a substatance which primilartily acts on cell division and bring growth. The word Kinetin is derived because of involvement in cell- division i.e cytokinesis. The term cytokinin was coined by Letham (1963)Practical application of BAP are as follows :

a) bIt promotes cell division, call enlargement and cell differentiation and brings about growth.

b) It promotes lateral buds and stimulates leaf expansion resulting in cell enlargement

c) Application of BAP slows down ageing, a phenomina called Senescence in leaves allowing those to remain green and actively photosynthesizing for longer period.

d) BAP stimulates Bolting (elongation of internodes prior to flowering) and flowering in some plants by causing cells in flower buds to divide and expand more rapidly than normal.

6. Ethephon (EP) :This is a synthetic plant growth regulator and acts like a growth retardant.

It releases a substance called ethane, which inhibits growth in plants.

Some of practical application of Ethephon are

a) Application of ethephon retards the elongation and promotes the lateral branches in tomato plants geranium and roses

b) It promotes the production of latex flow in rubber plants.

c) It induces the ripining of citrus fruits.

QUESTIONS

One marks Questions :

1. Define the term growth .2. What is meant by sigmoidal growth curve?3. Define growth curve?4. Name the apparatus used in determining growth in plants.5. What are phytohormones?6. Which are the two groups of growth regulators?7. Name any two phytohormones.8. Name the most naturally occurring auxin.9. What is growth inhibitors? Give an example.10. Expand 2,4-D?11. What is meant by parthenocarpy?12. Name the auxin which is used as weedicide.13. Name the fungus from which Gibberellin was discovered?14. Which harmone induces parthenocapy?15. Which harmone is applied for the for elongation of genetically dwarf plant?16. Name the hormone present in the liquid endosperme of coconut?17. Which hormone delays senescence?18. Name the gaseous hormone which stimulates the early ripening of fruits 19. Expand ABA.20. Which are the three phases of growth ?Two marks Questions :

1. Define the term growth. Mention the phases of growth.

2. Name any two phytohormones.

3. Name any two synthetic auxins. Give one practical application of each.

4. Mention any four commercial application of auxin.

5. Mention any four application of auxins in plants,6. Describe any two application of Gibberlins.

7. Write any two application if ethylene.

8. Write any four psychological effect og ethylene.

9. Mention any four uses of phytohormones in agriculture and horticulture.

10. What is photoperiodism? Classify plants based on its phenomina

11. Mention any two horticulture application of Gibberellins.

12. Write any four psychological effect of ABA

13. Write the commercial use of Cytokinin

14. Which are the important artificial growth regulator.

Five marks Questions :

1. Explain the region of growth in plants.2. What is sigmoid curve? Explain3. Describe an experiment to measure growth in plants.4. Discuss the growth of auzins in plants.5. Give four uses of plant hormone.6. What are cytokinins? Give their psychological role in plants.7. Write the physicological role of ABA and ethyelene in plants.8. Describe growth and its three phases.9. Explain the practical application of auxin.10. Describe the uses of phytohormones.11. Describe the practical application of synthetic growth regulator12. Give reason for the followinga. Pruning og plants results in their busy growthb. Removal of apical buds in plants favors the growth of lateral branches.c. A spry of Gibberllins over genetically dwarf plants induces their stem elongationQUESTIONS WITH MODEL ANSWERS.

One marks Question :

1. Define the term growth.Ans : Growth can be defined as permenant irrereversable change in size of cell organ or whole organism usually accoumpanied by an increase in dry weaight.

2. What is meant by sigmoid growth curve ?

Ans: The growth rate of plant against the time plotted on graph paper gives a S-shaped curve called Sigmoid curve or Growth curve.

3. Name the instrument that is used to measure the rate of growth .Ans: ArcAuxanometer.

4. Mention the phases of growth.Ans : The phases of growth are;

a) Phase of cell division

b) Phase of cell enlargement c) Phase of cell maturation

5. What are plant hormones?

ANs: Plant hormones are organic substances synthesized in minute quantities in one part of the plant body and transported to another part where they influence specific physiological process.

6. Name any two phytohormonesAns : a)Auxins

b) Gibberellins

7. Name the most naturally occurring auxin

Ans : Indole Acetic Acid (IAA)8. Which hormone is abbreviated as ABA ?

Ans : Abscisic Acid

9. Expand 2,4-D?

Ans: 2, 4- Dichlorophenoxy Acetic Acid

10. Name any two synthetic auxins.

Ans: 1) NAA( Napthalene Acetic Acid)

2) 2,4-D (2-4 Dichlorophenoxy acetic acid)

11. Name the naturally accouring phytohormones that causes apical dominance.

Ans: bIndole 3-Acetic acid

12. What is meant by parthenocrapy ?

Ans : Formation of seedless fruits without fertilization is called parthenocrapy

13. Name the auxin which is used as weedicide.Ans:2,4-D

14. Name the fungus from which Gibberllins was discovered ?Ans: Gibberella fujikuroi

15. What is result of addition of gibberllins to plants?

Ans: Gibberllins induce cell elongation and bolting

16. Which hormones induce parthenocrapy?

Ans: Auxins and Gibberllins17. Mention the hormone which brings about internodal elongationAns: Gibberllins

18. Who discovered cytokinins?Ans: Skoog, Miller and co- worker19. What is Richmond Lang effect?

Ans: Cytokinin has the property of delaying aging (senescence) of leaves and that effect is called Richmond Lang effect20. Which hormone delays senescence?Ans: Auxins

21. Name the gaseous hormone which stimulates the early ripining of fruits.

Ans Ethylene

22. Name the gaseous hormone which stimulates the early ripening of fruit.

Ans: Ethylene

23. Name the hormone present in the liquid endosperm of coconut.

Ans: Cytokinins.

24. Name the apparatus used in determining the growth of plnts.Ans: Arc,AuxanometerTwo marks questions :

1. What is growth ? Mention the phases of growth.

Ans: Growth can be defined as the permenatnt irrervesable change in size of a cell organ or organism usually accoumpanied by increase in dry weaight.

The phases of growth are : 1) Phase of cell formation2) Phase of cell enlargement

4) Phase of cell maturation

2. Name two synthetic auxins. Give one practical application of each.

Ans: Synthetic auxins

a) NAA- Napthelene acetic acid.

Practical Application : Initiates flowering in pineappleb) 2, 4-D (2,4-Dichlorophenoxy acetic acid)

Pratical Application : Used as Weedicide.3. Mention any four pratical application of auxinsAns: Four pratical application of auxins

a) Apical dominance and dormancy : Used for storage of potato tubers.

b) Production of parthenocarpic fruits : Used in the production of seedless fruits in grapes, water melon

c) Weedicide: To destroy weeds from cropfields, laws etc.

4. Mention any two horticulture application of Giberllins.Ans : Two horticulture application og Gibberllins are:

a) Elongation of stem : When gibberllins are sprayed on genetically dwarf plants (e,g:cabbage) that induces cell elongation

b) Bolting flowering : Plants with rosette of leaves attached to a short axis (e.g: Sugarbeat) when sprayed with gibberllins, show excessive elongation of the axis and start flowering. Stimulation of internodal growth just before reproduction s called bolting5. Write the psychological role of cytokinin.Ans: Psychological role of cytokinins,

a) It promotes abscission of leaves flowers and fruits

b) It prevents the elongation of shoots, keeps the embryos and buds dormant

c) Acts as stress hormone in plants when there is shortage of water salinity chilling and freezing temperature.

d) It promotes senescence of leaves.

Five Marks Question:1. Describe the experiment used to measure the linear growth in plants:

Ans: Aim : To determine the linear growth in plants with an arc auxanometer

Requirement : Arc auxanometer a young plotted plant a non flexible thread a light weight.

Procedure : Arc auxanometer has a pulley attached toit is a pointer which moves over an arc shaped scale. A well watered young potted plant is selected one end of a non flexible thread tied to the tip of the sem. The thread is then passed over the pulley and to the free end of the thread a light weight is attached to keep the thread under tension . The initial reading of the pointer on the scale is noted and the setup is left as such for few days for further observation As the stem grownin length the weight pulls the thread down

This results in the movement of pulley as well as the pointer on the scale The 1 reading on the scale is then noted down .Result: The difference bewen the initial reading and the final reading gives the growth of the plant noticed on the scale is then noted down.

Inference: The growth noticed on the scale is note the actual growth at the plant the magnification of the auxanometer and growth noticed on the scale the actual growth of plant can be calculated.

Eg : Radius of he pulley 2cm

Radius of pointer 20cm

Radius of pointer

Magnification = -------------------------------------

Radius of pulley

= 20/2 = 10cm

If the growth noticed on the scale 40cm

Actual growth = Growth noticed on the scale/ Magnification

= 40/10= 4cmSyllabus

Unit 4 Growth and Growth Regulators in Plants

SCIENTISTS

Flowers are produced

No flowering

No flowering

No flowering

