plant nutrition is the study of the chemical elements that are necessary for growth

8/6/2019 Plant Nutrition is the Study of the Chemical Elements That Are Necessary for Growth

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Plant nutrition is the study of the chemical elements that are necessary for growth. In 1972, E.Epstein defined 2 criteria for an element to be essential for plant growth: (1) in its absence the

plant is unable to complete a normal life cycle or (2) that the element is part of some essentialplant constituent or metabolite, this is all in accordance with Liebig's law of the minimum.[1]

There are 17 essential plant nutrients. Carbon and oxygen are absorbed from the air, while other

nutrients including water are obtained from the soil. Plants must obtain the following mineralnutrients from the growing media:[2]

y the primary macronutrients: nitrogen (N), phosphorus (P), potassium (K)y the three secondary macronutrients such as calcium (Ca), sulphur (S), magnesium (Mg).y the macronutrient Silicon (Si)y and micronutrients or trace minerals: boron (B), chlorine (Cl), manganese (Mn), iron

(Fe), zinc (Zn), copper (Cu), molybdenum (Mo), nickel (Ni), selenium (Se), and sodium(Na).

The macronutrients are consumed in larger quantities and are present in plant tissue in quantities

from 0.2% to 4.0% (on a dry matter weight basis). Micronutrients are present in plant tissue inquantities measured in parts per million, ranging from 5 to 200 ppm, or less than 0.02% dry

weight.[3]

Most soil conditions across the world can provide plants with adequate nutrition and do not

require fertilizer for a complete life cycle. However, man can artificially modify soil through theaddition offertilizerto promote vigorous growth and increase yield. The plants are able to obtain

their required nutrients from the fertilizer added to the soil. A colloidal carbonaceous residue,known as humus, can serve as a nutrient reservoir.[4] Besides lack of water and sunshine, nutrient

deficiency is a major growth limiting factor.

Nutrient uptake in the soil is achieved by cation exchange, where in root hairs pumphydrogenions (H+) into the soil throughproton pumps. These hydrogen ions displace cations

attached to negatively charged soil particles so that the cations are available for uptake by theroot.

Plant nutrition is a difficult subject to understand completely, partially because of the variation

between different plants and even between different species or individuals of a given clone. Anelement present at a low level may cause deficiency symptoms, while the same element at a

higher level may cause toxicity. Further, deficiency of one element may present as symptoms oftoxicity from another element. An abundance of one nutrient may cause a deficiency of another

nutrient. Also a lowered availability of a given nutrient, such as SO24

can affect the uptake ofanother nutrient, such as NO

3

. Also, K

+uptake can be influenced by the amount NH

4

+

available.[4]

The root, especially the root hair, is the most essential organ for the uptake of nutrients. The

structure and architecture of the root can alter the rate of nutrient uptake. Nutrient ions aretransported to the center of the root, the stele in order for the nutrients to reach the conducting

tissues, xylem and phloem.[4]

The Casparian strip, a cell wall outside of the stele but within theroot, prevents passive flow of water and nutrients to help regulate the uptake of nutrients and


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water.[4]

Xylem moves water and inorganic molecules within the plant andphloem counts organicmolecule transportation. Water potential plays a key role in a plants nutrient uptake. If the water

potential is more negative within the plant than the surrounding soils, the nutrients will movefrom the more higher solute (soil) concentration to lower solute concentration (plant).

There are 3 fundamental ways plants uptake nutrients through the root: 1.) simple diffusion,occurs when a nonpolar molecule, such as O2, CO2, and NH3 that follow a concentrationgradient, can passively move through the lipid bilayer membrane without the use of transport

proteins. 2.) facilitated diffusion, is the rapid movement of solutes or ions following aconcentration gradient, facilitated by transport proteins. 3.) Active transport, is the active

transport of ions or molecules against a concentration gradient that requires an energy source,usually ATP, to pump the ions or molecules through the membrane.

[4]

Nutrients are moved inside a plant to where they are most needed. For example, a plant will try

to supply more nutrients to its younger leaves than its older ones. So when nutrients are mobile,the lack of nutrients is first visible on older leaves. However, not all nutrients are equally mobile.

When a less mobile nutrient is lacking, the younger leaves suffer because the nutrient does notmove up to them but stays lower in the older leaves. Nitrogen, phosphorus, and potassium are

mobile nutrients, while the others have varying degrees of mobility. This phenomenon is helpfulin determining what nutrients a plant may be lacking.

A symbiotic relationship may exist with 1.) Nitrogen-fixing bacteria, like rhizobia which areinvolved with nitrogen fixation, and 2.) mycorrhiza, which help to create a larger root surface

area. Both of these mutualistic relationships enhance nutrient uptake.[4]

Though nitrogen is plentiful in the Earth's atmosphere, relatively few plants engage in nitrogenfixation (conversion of atmospheric nitrogen to a biologically useful form). Most plants therefore

require nitrogen compounds to be present in the soil in which they grow. These can either besupplied by decaying matter, nitrogen fixing bacteria, animal waste, or through the agricultural

application of purpose made fertilizers.

Hydroponics, is growing plants in a water-nutrient solution without the use of nutrient-rich soil.It allows researchers and home gardeners to grow their plants in a controlled environment. The

most common solution, is the Hoagland Solution, developed by D. R. Hoagland in 1933, thesolution consists of all the essential nutrients in the correct proportions necessary for most plant

growth.[4]

An aerator is used to prevent an anoxic event or hypoxia. Hypoxia can affect nutrientuptake of a plant because without oxygen present, respiration becomes inhibited within the root

cells. TheNutrient film technique is a variation of hydroponic technique. The roots are not fullysubmerged which allows for adequate aeration of the roots, while a "film" thin layer of nutrient

rich water is pumped through the system to provide nutrients and water to the plant.

[edit] Processes important to plant nutrition


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Plants uptake essential elements from the soil through theirroots and from the air (mainlyconsisting of carbon and oxygen) through theirleaves.

In the leaves, transpiration occurs, where stomata open to take in carbon dioxide and expel

oxygen that drives the movement of water and nutrients to the plant[4]

Green plants obtain their

carbohydrate supply from the carbon dioxide in the air by the process ofphotosynthesis.

[edit] Functions of nutrients

Each of these nutrients is used in a different place for a different essential function.[5]

[edit] Macro nutrients

Carbon

Carbon forms the backbone of many plantsbiomolecules, including starches and

cellulose. Carbon is fixed throughphotosynthesis from the carbon dioxide in the air andis a part of the carbohydrates that store energy in the plant.

Hydrogen

Hydrogen also is necessary for building sugars and building the plant. It is obtained

almost entirely from water. Hydrogen ions are imperative for a proton gradient to helpdrive the electron transport chain in photosynthesis and for respiration.[4]

Oxygen

Oxygen is necessary forcellular respiration. Cellular respiration is the process ofgenerating energy-rich adenosine triphosphate (ATP) via the consumption of sugars made

in photosynthesis. Plants produce oxygen gas during photosynthesis to produce glucosebut then require oxygen to undergo aerobic cellular respiration and break down this

glucose and produce ATP.

Phosphorus

Phosphorus is important in plantbioenergetics. As a component ofATP, phosphorus is

needed for the conversion of light energy to chemical energy (ATP) duringphotosynthesis. Phosphorus can also be used to modify the activity of various enzymes

byphosphorylation, and can be used forcell signaling. Since ATP can be used for thebiosynthesis of many plantbiomolecules, phosphorus is important for plant growth and

flower/seed formation. Phosphate esters make up DNA, RNA, and phospholipids. Mostcommon in the form of polyprotic phosphoric acid (H3PO4) in soil, but it is taken up most

readily in the form of H2PO4. Phosphorus is limited in most soils because it is releasedvery slowly from insoluble phosphates. Under most environmental conditions it is the

limiting element because of its small concentration in soil and high demand by plants and


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microorganisms. Plants can increase phosphorus uptake by a mutualism withmycorrhiza.

[4]

A Phosphorus deficiency in plants is characterized by an intense green coloration inleaves. If the plant is experiencing high phosphorus deficiencies the leaves may become

denatured and show signs of necrosis. Occasionally the leaves may appear purple from an

accumulation of anthocyanin. Because phosphorus is a mobile nutrient, older leaves willshow the first signs of deficiency.High phosphorus content fertilizers, such as bone meal, is useful to apply to perennials to

help with successful root formation.[4]

Potassium

Potassium regulates the opening and closing of the stomata by a potassium ion pump.Since stomata are important in water regulation, potassium reduces water loss from the

leaves and increases drought tolerance. Potassium deficiency may cause necrosis orinterveinalchlorosis. K+ is highly mobile and can aid in balancing the anion charges

within the plant. It also has high solubility in water and leaches out of soils that rocky orsandy that can result in potassium deficiency. It serves as an activator of enzymes used in

photosynthesis and respiration[4] Potassium is used to build cellulose and aids inphotosynthesis by the formation of a chlorophyll precursor.

Potassium deficiency may result in higher risk of pathogens, wilting, chlorosis, brownspotting, and higher chances of damage from frost and heat.

Nitrogen

Nitrogen is an essential component of all proteins.Nitrogen deficiency most often resultsin stunted growth, slow growth, and chlorosis. Nitrogen deficient plants will also exhibit

a purple appearance on the stems, petioles and underside of leaves from an accumulationof anthocyanin pigements[4]

Most of the nitrogen taken up by plants is from the soil in the forms of NO3

. Aminoacids and proteins can only be built from NH4

+ so NO3must be reduced. Under many

agricultural settings, nitrogen is the limiting nutrient of high growth. Some plants requiremore nitrogen than others, such as corn (Zea mays). Because nitrogen is mobile, the older

leaves exhibit chlorosis and necrosis earlier than the younger leaves. Soluble forms ofnitrogen are transported as amines and amides

[4]

Sulphur

Sulphur is a structural component of some amino acids and vitamins, and is essential inthe manufacturing ofchloroplasts.

Calcium

Calcium regulates transport of other nutrients into the plant and is also involved in theactivation of certain plant enzymes. Calcium deficiency results in stunting.


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Magnesium

Magnesium is an important part ofchlorophyll, a critical plantpigment important inphotosynthesis. It is important in the production ofATP through its role as an enzyme

cofactor. There are many other biological roles for magnesiumsee Magnesium in

biological systems for more information. Magnesium deficiency can result ininterveinalchlorosis.

Silicon

Silicon is deposited in cell walls and contributes to its mechanical properties including

rigidity and elasticity[citation needed]

[edit] Micronutrients

Iron

Iron is necessary for photosynthesis and is present as an enzyme cofactor in plants. Irondeficiency can result in interveinalchlorosis and necrosis.

Molybdenum

Molybdenum is a cofactor to enzymes important in building amino acids.

Boron

Boron is important for binding of pectins in the RGII region of the primary cell wall,

secondary roles may be in sugar transport, cell division, and synthesizing certainenzymes. Boron deficiency causes necrosis in young leaves and stunting.

Copper

Copper is important for photosynthesis. Symptoms for copper deficiency include

chlorosis. Involved in many enzyme processes.Necessary for properphotosythesis.Involved in the manufacture of lignin (cell walls).Involved in grain

production.

Manganese

Manganese is necessary for building the chloroplasts. Manganese deficiency may result

in coloration abnormalities, such as discolored spots on the foliage.

Sodium

Sodium is involved in the regeneration ofphosphoenolpyruvate in CAM and C4 plants. It

can also substitute for potassium in some circumstances.


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Zinc

Zinc is required in a large number of enzymes and plays an essential role in DNAtranscription. A typical symptom of zinc deficiency is the stunted growth of leaves,

commonly known as "little leaf" and is caused by the oxidative degradation of the growth

hormone auxin.

Nickel

In higher plants, Nickel is essential for activation ofurease, an enzyme involved withnitrogen metabolism that is required to process urea. Without Nickel, toxic levels of urea

accumulate, leading to the formation of necrotic lesions. In lower plants, Nickel activatesseveral enzymes involved in a variety of processes, and can substitute for Zinc and Iron

as a cofactor in some enzymes.[2]

Chlorine

Chlorine is necessary forosmosis and ionic balance; it also plays a role inphotosynthesis.

Cobalt has proven to be beneficial to at least some plants, but is essential in others, such as

legumes where it is required fornitrogen fixation for the symbiotic relationship it has withnitrogen-fixing bacteria. Vanadium may be required by some plants, but at very low

concentrations. It may also be substituting formolybdenum. Selenium and sodium may also bebeneficial. Sodium can replace potassium's regulation of stomatal opening and closing

[4]

WHAT IS PLANT NUTRITION?

Plants use inorganic minerals for nutrition, whether grown in the field or in a container. Complexinteractions involving weathering of rock minerals, decaying organic matter, animals, and

microbes take place to form inorganic minerals in soil. Roots absorb mineral nutrients as ions insoil water. Many factors influence nutrient uptake for plants. Ions can be readily available to

roots or could be "tied up" by other elements or the soil itself. Soil too high in pH (alkaline) ortoo low (acid) makes minerals unavailable to plants.

FERTILITY OR NUTRITION

The term "fertility" refers to the inherent capacity of a soil to supply nutrients to plants in

adequate amounts and in suitable proportions. The term "nutrition" refers to the interrelated stepsby which a living organism assimilates food and uses it for growth and replacement of tissue.

Previously, plant growth was thought of in terms of soil fertility or how much fertilizer should beadded to increase soil levels of mineral elements. Most fertilizers were formulated to account for

deficiencies of mineral elements in the soil. The use of soilless mixes and increased research innutrient cultures and hydroponics as well as advances in plant tissue analysis have led to a

broader understanding of plant nutrition. Plant nutrition is a term that takes into account theinterrelationships of mineral elements in the soil or soilless solution as well as their role in plant


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growth. This interrelationship involves a complex balance of mineral elements essential andbeneficial for optimum plant growth.

ESSENTIAL VERSUS BENEFICIAL

The term essential mineral element (or mineral nutrient) was proposed by Arnon and Stout(1939). They concluded three criteria must be met for an element to be considered essential.

These criteria are: 1. A plant must be unable to complete its life cycle in the absence of themineral element. 2. The function of the element must not be replaceable by another mineral

element. 3. The element must be directly involved in plant metabolism. These criteria areimportant guidelines for plant nutrition but exclude beneficial mineral elements. Beneficial

elements are those that can compensate for toxic effects of other elements or may replacemineral nutrients in some other less specific function such as the maintenance of osmotic

pressure. The omission of beneficial nutrients in commercial production could mean that plantsare not being grown to their optimum genetic potential but are merely produced at a subsistence

level. This discussion of plant nutrition includes both the essential and beneficial mineral

elements.

WHAT ARE THE MINERAL ELEMENTS?

There are actually 20 mineral elements necessary or beneficial for plant growth. Carbon (C),hydrogen (H), and oxygen (O) are supplied by air and water. The six macronutrients, nitrogen

(N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) are requiredby plants in large amounts. The rest of the elements are required in trace amounts

(micronutrients). Essential trace elements include boron (B), chlorine (Cl), copper (Cu), iron(Fe), manganese (Mn), sodium (Na), zinc (Zn), molybdenum (Mo), and nickel (Ni). Beneficial

mineral elements include silicon (Si) and cobalt (Co). The beneficial elements have not beendeemed essential for all plants but may be essential for some. The distinction between beneficial

and essential is often difficult in the case of some trace elements. Cobalt for instance is essentialfor nitrogen fixation in legumes. It may also inhibit ethylene formation (Samimy, 1978) and

extend the life of cut roses (Venkatarayappa et al., 1980). Silicon, deposited in cell walls, hasbeen found to improve heat and drought tolerance and increase resistance to insects and fungal

infections. Silicon, acting as a beneficial element, can help compensate for toxic levels ofmanganese, iron, phosphorus and aluminum as well as zinc deficiency. A more holistic approach

to plant nutrition would not be limited to nutrients essential to survival but would includemineral elements at levels beneficial for optimum growth. With developments in analytical

chemistry and the ability to eliminate contaminants in nutrient cultures, the list of essentialelements may well increase in the future.

THE MINERAL ELEMENTS IN PLANT PRODUCTION

The use of soil for greenhouse production before the 1960s was common. Today a few growersstill use soil in their mixes. The bulk of production is in soilless mixes. Soilless mixes must

provide support, aeration, nutrient and moisture retention just as soils do, but the addition offertilizers or nutrients are different. Many soilless mixes have calcium, magnesium, phosphorus,


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sulfur, nitrogen, potassium and some micronutrients incorporated as a pre-plant fertilizer.Nitrogen and potassium still must be applied to the crop during production. Difficulty in

blending a homogenous mix using pre-plant fertilizers may often result in uneven crops andpossible toxic or deficient levels of nutrients. Soilless mixes that require addition of micro and

macronutrients applied as liquid throughout the growth of the crop, may actually give the grower

more control of his crop. To achieve optimum production, the grower can adjust nutrient levelsto compensate for other environmental factors during the growing season. The absorption ofmineral ions is dependent on a number of factors in addition to weather conditions. These

include the cation exchange capacity or CEC and the pH or relative amount of hydrogen (H+) orhydroxyl ions (OH-) of the growing medium, and the total alkalinity of the irrigation water.

CEC OR CATION EXCHANGE CAPACITY

The Cation Exchange Capacity refers to the ability of the growing medium to hold exchangeablemineral elements within its structure. These cations include ammonium nitrogen, potassium,

calcium, magnesium, iron, manganese, zinc and copper. Peat moss and mixes containing bark,

sawdust and other organic materials all have some level of cation exchange capacity.

pH: WHAT DOES IT MEAN?

The term pH refers to the alkalinity or acidity of a growing media water solution. This solutionconsists of mineral elements dissolved in ionic form in water. The reaction of this solution

whether it is acid, neutral or alkaline will have a marked effect on the availability of mineralelements to plant roots. When there is a greater amount of hydrogen H+ ions the solution will be

acid (7.0). A balance ofhydrogen to hydroxyl ions yields a pH neutral soil (=7.0). The range for most crops is 5.5 to 6.2

or slightly acidic. This creates the greatest average level for availability for all essential plantnutrients. Extreme fluctuations of higher or lower pH can cause deficiency or toxicity of

nutrients.

THE ELEMENTS OF COMPLETE PLANT NUTRITION

The following is a brief guideline of the role of essential and beneficial mineral nutrients that are

crucial for growth. Eliminate any one of these elements, and plants will display abnormalities ofgrowth, deficiency symptoms, or may not reproduce normally.

Macronutrients

Nitrogen is a major component of proteins, hormones, chlorophyll, vitamins and enzymesessential for plant life. Nitrogen metabolism is a major factor in stem and leaf growth (vegetative

growth). Too much can delay flowering and fruiting. Deficiencies can reduce yields, causeyellowing of the leaves and stunt growth.

Phosphorus is necessary for seed germination, photosynthesis, protein formation and almost all

aspects of growth and metabolism in plants. It is essential for flower and fruit formation. Low pH


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(


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Boron is necessary for cell wall formation, membrane integrity, calcium uptake and may aid inthe translocation of sugars. Boron affects at least 16 functions in plants. These functions include

flowering, pollen germination, fruiting, cell division, water relationships and the movement ofhormones. Boron must be available throughout the life of the plant. It is not translocated and is

easily leached from soils. Deficiencies kill terminal buds leaving a rosette effect on the plant.

Leaves are thick, curled and brittle. Fruits, tubers and roots are discolored, cracked and fleckedwith brown spots.

Zinc is a component of enzymes or a functional cofactor of a large number of enzymes includingauxins (plant growth hormones). It is essential to carbohydrate metabolism, protein synthesis and

internodal elongation (stem growth). Deficient plants have mottled leaves with irregular chloroticareas. Zinc deficiency leads to iron deficiency causing similar symptoms. Deficiency occurs on

eroded soils and is least available at a pH range of 5.5 - 7.0. Lowering the pH can render zincmore available to the point of toxicity.

Copper is concentrated in roots of plants and plays a part in nitrogen metabolism. It is a

component of several enzymes and may be part of the enzyme systems that use carbohydratesand proteins. Deficiencies cause die back of the shoot tips, and terminal leaves develop brown

spots. Copper is bound tightly in organic matter and may be deficient in highly organic soils. It isnot readily lost from soil but may often be unavailable. Too much copper can cause toxicity.

Molybdenum is a structural component of the enzyme that reduces nitrates to ammonia. Withoutit, the synthesis of proteins is blocked and plant growth ceases. Root nodule (nitrogen fixing)

bacteria also require it. Seeds may not form completely, and nitrogen deficiency may occur ifplants are lacking molybdenum. Deficiency signs are pale green leaves with rolled or cupped

margins.

Chlorine is involved in osmosis (movement of water or solutes in cells), the ionic balancenecessary for plants to take up mineral elements and in photosynthesis. Deficiency symptoms

include wilting, stubby roots, chlorosis (yellowing) and bronzing. Odors in some plants may bedecreased. Chloride, the ionic form of chlorine used by plants, is usually found in soluble forms

and is lost by leaching. Some plants may show signs of toxicity if levels are too high.

Nickel has just recently won the status as an essential trace element for plants according to theAgricultural Research Service Plant, Soil and Nutrition Laboratory in Ithaca, NY. It is required

for the enzyme urease to break down urea to liberate the nitrogen into a usable form for plants.Nickel is required for iron absorption. Seeds need nickel in order to germinate. Plants grown

without additional nickel will gradually reach a deficient level at about the time they mature andbegin reproductive growth. If nickel is deficient plants may fail to produce viable seeds.

Sodium is involved in osmotic (water movement) and ionic balance in plants.

Cobalt is required for nitrogen fixation in legumes and in root nodules of nonlegumes. Thedemand for cobalt is much higher for nitrogen fixation than for ammonium nutrition. Deficient

levels could result in nitrogen deficiency symptoms.


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Silicon is found as a component of cell walls. Plants with supplies of soluble silicon producestronger, tougher cell walls making them a mechanical barrier to piercing and sucking insects.

This significantly enhances plant heat and drought tolerance. Foliar sprays of silicon have alsoshown benefits reducing populations of aphids on field crops. Tests have also found that silicon

can be deposited by the plants at the site of infection by fungus to combat the penetration of the

cell walls by the attacking fungus. Improved leaf erectness, stem strength and prevention ordepression of iron and manganese toxicity have all been noted as effects from silicon. Silicon hasnot been determined essential for all plants but may be beneficial for many.

In its purest form, the term "biotechnology" refers to the use of living organisms or theirproducts to modify human health and the human environment. Prehistoric biotechnologists did

this as they used yeast cells to raise bread dough and to ferment alcoholic beverages, andbacterial cells to make cheeses and yogurts and as they bred their strong, productive animals to

make even stronger and more productive offspring.

Throughout human history, we have learned a great deal about thedifferent organisms that our ancestors used so effectively. The

marked increase in our understanding of these organisms and theircell products gains us the ability to control the many functions ofvarious cells and organisms. Using the techniques of gene splicing

and recombinant DNA technology, we can now actually combine thegenetic elements of two or more living cells. Functioning lengths of

DNA can be taken from one organism and placed into the cells ofanother organism. As a result, for example, we can cause bacterial cells to produce human

molecules. Cows can produce more milk for the same amount of feed. And we can synthesizetherapeutic molecules that have never before existed.


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The tenurebiotechnology refers to the use of systematic techniques, together with geneticengineering, to urge or cgange plants, animals, and microorganisms. In the most simple forms,

biotechnology has been in use for millennia. For example, Middle Easterners who trained andbred deer, antelope, and sheep as early as 18,000 B.C.E.; Egyptians who done booze in 4000

B.C.E.; and Louis Pasteur, who grown pasteurization in 1861, all used biotechnology. In new

years, however, food biotechnology has turn synonymous with the conditions geneticallyengineered dishes and genetically mutated mammal (GMO).

Traditional biotechnology uses techniques such as crossbreeding, fermentation, and enzymatictreatments to furnish preferred changes in plants, animals, and foods. Crossbreeding plants or

animals involves the resourceful thoroughfare of fascinating genes from a single era to another.Microbial distillation is used in creation booze and alternative alcoholic beverages, yogurt, and

most cheeses and breads. Using enzymes as food additives is an a single more normal form ofbiotechnology. For example, papain, an chemical substance performed from papaya fruit, is used

to tenderize beef and explain beverages.

Genetic Engineering

The DNA contained in genes determines hereditary characteristics. Modifying DNA to remove,

add, or change genetic report is called genetic alteration or genetic engineering. In the early1980s, scientists grown recombinant DNA techniques which authorised them to remove DNA

from a single class and insert it in to another. Refinements in these techniques have authorisedmarker of specific genes inside ofDNAand the send of which sold gene method ofDNA in to

an a single more species. For example, the genes obliged for producing insulin in humans havebeen removed and extrinsic in to bacteria. The insulin which is afterwards constructed by these

bacteria, which is matching to tellurian insulin, is afterwards removed and since to people whohave diabetes. Similarly, the genes which furnish chymosin, an chemical substance which is

concerned in cheese manufacturing, have additionally been extrinsic in to bacteria. Now, insteadof carrying to remove chymosin from the stomachs of cows, it is done by bacteria. This sort of

focus of genetic engineering has not been really controversial. However, applications involvingthe use of plants have been some-more controversial.

Among the initial blurb applications of genetically engineered dishes was a chopped tomatoes inwhich the gene which produces the chemical substance obliged for softening was incited off. The

chopped tomatoes could afterwards be authorised to rise upon the vine yet removing as wellsoothing to be finished and shipped. As of 2002, over forty food crops had been mutated

regulating recombinant DNA technology, together with pesticide-resistant soybeans, virus-resistant squash, frost-resistant strawberries, corn and potatoes containing a healthy pesticide,

and rice containing beta-carotene. Consumer negativity toward biotechnology is increasing, notusually in the United States, yet additionally in the United Kingdom, Japan, Germany, and

France, notwithstanding increasing consumer hold of biotechnology. The element objections tobiotechnology and dishes constructed regulating genetic alteration are: regard about probable

mistreat to tellurian illness (such as allergic responses to a foreign gene), probable disastrousstroke to the environment, a ubiquitous confusion about the unnatural standing of

biotechnology, and eremite concerns about modification.

Biotechnology in Animals


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The most argumentative applications of biotechnology engage the use of animals and the send ofgenes from animals to plants. The initial animal-based focus of biotechnology was the

capitulation of the use f bacterially Scientists extrinsic daffodil genes and alternative geneticelement in to typical rice to have this golden rice. The outcome is a aria of rice which provides

vitamin A, a nutritious blank from the diets of most people who rely upon rice as a food staple.

[AP/Wide World Photos.Reproduced by permission.]Scientists extrinsic daffodil genes andalternative genetic element in to typical rice to have this golden rice. The outcome is a aria ofrice which provides vitamin A, a nutritious blank from the diets of most people who rely upon

rice as a food staple. [AP/Wide World Photos.Reproduced by permission.]constructed cowsomatotropin (bST) in dairy cows. Bovine somatotropin, a of course occurring hormone,

increases divert production. This focus has not been commercially successful, however,essentially since of the expense. The cloning of animals is an a single more intensity focus of

biotechnology. Most experts hold which animal applications of biotechnology will start solemnlysince of the amicable and reliable concerns of consumers.

Concerns about Food Production

Some concerns about the use of biotechnology for food prolongation embody probable allergicreactions to the eliminatedprotein. For example, if a gene from Brazil nuts which produces an

allergen were eliminated to soybeans, an part icular who is allergic to Brazil nuts competenceright away additionally be allergic to soybeans. As a result, companies in the United States

which rise genetically engineered dishes contingency denote to the U.S. Food and DrugAdministration (FDA) which they did not send proteins which could outcome in food allergies.

When, in fact, a association attempted to send a gene from Brazil nuts to soybeans, thecompanys tests suggested which they had eliminated a gene for an allergen, and work upon the

plan was halted. In 2000 a code of taco shells was detected to enclose a accumulation ofgenetically engineered corn which had been authorized by the FDA for use in animal feed, yet

not for tellurian consumption. Although multiform antibiotechnology groups used this situationas an e.g. of intensity allergenicity stemming from the use of biotechnology, in this box the

protein constructed by the genetically mutated gene was not an allergen. This situationadditionally demonstrated the difficulties in gripping lane of a genetically mutated food which

looks matching to the unmodified food. Other concerns about the use of recombinant DNArecord embody intensity waste of biodiversity and disastrous impacts upon alternative aspects of

the environment.

Safety and Labeling

In the United States, the FDA has ruled which dishes constructed yet biotechnology need the

same capitulation routine as all alternative food, and which there is no fundamental illness risk inthe use of biotechnology to rise plant food products. Therefore, no tag is compulsory simply tobrand dishes as products of biotechnology. Manufacturers bear the weight of explanation for the

reserve of the food. To support them with this, the FDA grown a decision-tree proceed whichallows food processors to expect reserve concerns and know when to deliberate the FDA for

guidance. The preference tree focuses upon toxicants which have been evil of any class involved;the intensity for transferring food allergens from a single food source to another; the

thoroughness and bioavailability of nutrients in the food; and the reserve and nutritive worth ofnewly introduced proteins.


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Labeling of genetically mutated dishes has sparked a single more debate. Labels have beencompulsory upon food constructed by biotechnology to surprise consumers of any intensity

illness or reserve risk. For example, a tag is compulsory if a intensity allergen is introduced in toa food product. A tag is additionally compulsory if a food is remade so which the nutritious calm

no longer resembles the strange food. For example, supposed golden rice has been genetically

engineered to have a aloft thoroughness of beta-carotene than unchanging rice, and to illustrate itcontingency be enclosed upon the label. In reply to consumer demands, regulators in Englandhave instituted imperative labeling laws for all finished dishes and menus containing genetically

mutated ingredients. Similar yet reduction limiting laws have been instituted in Japan. In Canada,the process upon labeling has remained identical to which of the United States.

Some consumer advocates say which not requiring a tag upon all genetically mutated dishes

violates consumers right to have sensitive food choices, and most producers of sure foods, suchas dishes containing soy protein, right away embody the tenure non-GMO upon the tag to

prove which the product does not enclose genetically mutated ingredients.

The focus of recombinant DNA record to foods, ordinarily called biotechnology, might benoticed as an prolongation of normal cross-breeding and distillation techniques. The record

enables scientists to send genetic element from a single class to another, and might furnish foodcrops and animals which have been opposite than those performed regulating normal techniques.

The FDA has determined procedures for capitulation of food products made regulatingrecombinant DNA record which need food producers to denote the reserve of their products. The

American Dietetic Association, the American Medical Association, and the World HealthOrganization have any adopted statements which techniques of biotechnology might have the

intensity to urge the food supply. These organizations and others admit which long-term illnessand environmental impacts of the record have been not known, and they inspire redundant

monitoring of intensity impacts.\

Introduction

The origin of the flowering plants was described by Charles Darwin as "that abominable

mystery". Flowering plants are the dominant plants on the earth today with an estimated quarterof a million species. Unlike lower plants like ferns and seaweeds which rely on spores to invade

new habitats, flowering plants are dispersed by seeds and this undoubtedly accounts for theirsuccess. Lower plants alternate in their life cycle between distinct sporophyte and gametophyte

stages. While these phases can be recognised in flowering plants as well, an understanding of

this is not required for CAPE Biology and these concepts are best ignored at this level.

Flower structure

The flower is simply a collection of highly modified leaves. The outermost series is

collectively termed the perianth and comprises sepals, which protect the developingflower, and petals, which often serve to attract pollinators. Within the perianth lie the


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actual reproductive organs. The stamens produce pollen from which the male gametesare ultimately derived. The carpels contain an ovary with ovules in which the female

gametes develop.

Following the transfer of pollen to the stigma or receptive surface of the carpel, in a

process called pollination, nuclei from the pollen will ultimately fuse with nucleiwithin the ovule's embryosac to form the seed.

In some flowering plants all

the perianth parts aresimilar; there are noseparate sepals and petals.

This can often be seen inlily-like plants like the

Spider Lily(Hymenocalliscaribaea).

The flowering plants show great variation in flower structure and these characteristics are central

to flowering plant classification. In most cases, flowers are not borne singly but grouped on acommon stalk and termed an inflorescence. Various inflorescence types are recognised and

while these do not concern us at this level be aware that these are very important inclassification.


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Sometimes the flowerhas closely associated

with it a prominent(often coloured) leaf

termed a bract. In

bougainvillea (left)these bracts are moreattractive than the

actual flower which ispale and inconspicuous.

Similarly, red bractsconstitute the most

conspicuous part of theinflorescence of the red

ginger lily (right).

Overview ofsexual reproduction

The details of pollen grain development and embryosac formation will not be discussed here as

these are well covered in all textbooks. Some points, however, are worth emphasising.

y In both pollen and ovule development, meiosis occurs which not only halves thechromosome complement of cells but involves crossing over and so a reshuffling of

genes, ensuring genetic recombination.

y Unlike other seed plants, the ovules are completely sealed within the carpel. This meansthat the pollen tube must actually bore its way down through the style into the ovary and

this has led to the evolution in flowering plants of self incompatibility mechanisms toprevent the entry of "undesirable" pollen.

y The flowering plants are unique in having a double fertilisation event. One nucleus fromthe pollen grain will fuse with the egg to form the diploid zygote which develops into a

minature plant, the embryo. More unusual is the fact that a second nucleus from thepollen will fuse with 2 polar nuclei of the embryosac to form a triploid cell which

develops into the endosperm, a tissue that will provide nutrition for the embryo. Theseed that results then comprises the embryo, a minature plant ready to start a life of its

own, with reserve materials either in a surrounding endosperm or transferred to theembryo's cotyledons, all within a tough seed coat.


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y One final unique feature of sexual reproduction in flowering plants is the development offruit. Following fertilisation, as each ovule form a seed, the ovary swells to form the

fruit. The biologist's definition of a fruit is simply an organ for dispersing seeds. This isquite different to the layman's concept of a fruit as something soft, juicy and edible. Fruit

may split or remain intact. They can be hard and dry like a calabash or fleshy like a

tomato or a cucumber. There is a complex system of recognised fruit types but you neednot worry about these in this course.

Promotion of cross-fertilisation

To ensure the long term survival of any species it is advantageous to have a large and variedpopulation on which natural selection can act. Such variability is promoted by cross-fertilisation

and reduced by self-fertilisation. Not surprisingly flowering plants have evolved a number ofmechanisms which maximise cross-pollination.

1. Separation of thesex organs

Some plants have unisexual flowers (i.e. contain either carpels or stamens but not both) ratherthan bisexual flowers. In dioeciousspecies, plants are either male or female (e.g. nutmeg,

marijuana). In monoeciousspecies, there are separate male and female flowers but on the sameplant (e.g. castor oil, breadfruit, corn, pumpkin).

Female & male flowers ofJatrophaintegerrima, a common garden shrub

in the Caribbean

Castor oil,Ricinuscommunis


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2. Timing mechanismsSex organs may mature at different times.

Protandry is where the anthers maturefirst while protogyny is where the stigma

is receptive before the anthers mature.

Both avocado and soursop areprotogynous. The Anthurium bloom,which is not a flower but an inflorescence

or collection of flowers, is anotherexample. The fleshy spadix feels wet

when the minute female flowers are ripeand dry and powdery when the pollen is

being shed. Male and female parts arenever ripe together.

Soursop flower with perianth (left),

without perianth (centre), with anthersshed (right)

3. Specialised pollination mechanismsMany plants have highly specialised pollination

mechanisms, often adapted to a single insect, bird or batpollinator. The highly specialised flower structure and

manipulation of the behaviour of the vector ensure cross-pollination. Click here to see flowers with insect eyes!

Several Aristolochiaflower types

Aristolochia, Dutchman's pipe,is a woody vine with severalspecies native to the Caribbean,

all with strange, bent, tubularflowers. Flies are attracted by a

putrid scent emitted by theflower and enter its tunnel-like

interior. Downward pointinghairs allow them to proceed

further but not escape. The

flowers are protogynous so onthis first day the stigmas arereceptive but no pollen is shed.

On Day 2, the stigmas witherand the pollen is now shed,

coating the entrapped flies. Thenext day the hairs blocking the

flies' escape whither, setting


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the "prisoners" free. They nowvisit a new freshly-open,

"fragrant" flower. The story isrepeated again but on arrival

they bring pollen to the

receptive stigmas of these Day1 flowers and so achieve cross-pollination!

Orchids also provide good

examples of highly evolvedflower-pollinator relationships

- the stuff of natural historydocumentaries.

4. HeterostylyIn some species a plant bears one of two

morphological forms of a flower. Flowersmay have long styles with anthers near

the flower base (pin form) or short styleswith anthers borne on high (thrum form).

These arrangements prevent selfing when

a pollinator visits and ensures cross-pollination between plants with thedifferent flower types. The Red Cordia,

Cordiasebestena, (right) shows this.


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5. Self incompatibility

When a pollen grain germinates on a stigma of the same species arecognition process takes place. This involves molecules from the

stigma entering the pollen grain and vice versa. This process isunder genetic control and results in pollen from the same plant or a

different plant of similar genetic make-up being rejected. Thepollen grain may be prevented from germinating or the growth ofits tube may be inhibited within the style. Many plants including

cabbage and tobacco show this.

Asexual reproduction

Sexual reproduction in flowering plants involves meiosis and the fusion of gametes, usually fromdifferent plants, and results in seedlings which differ from their parents. In asexual reproduction,

exact copies of the parent plant result as the new plants are formed simply by mitosis. Sometimesflowers are involved in this process but usually only the vegetative parts of the plant are involved

and so this is termed vegetative reproduction.


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Plants have a

range of

perennating

organs, whichstore reserves and

are produced toenable the plant to

tide over periodsof unfavourable

environmentalconditions, e.g. the

dry season in thetropics, winter in

temperate regions.Examples of these

are the rhizomes

(undergroundstems) of ginger,the stem tubers of

English potato, thecorms (vertical

stem tubers) ofeddo, the root

tubers of yam andsweet potato and

the bulbs of onionsand lily-like

plants. These canbe used as a means

of propagating theplant in question.

corm bulb

Plants may also send out creeping branches or runners (Water lettuce), or may produceadventitious buds along the edges of leaves (Bryophyllum sp.). Most Agave spp. (Maypole,

Dagger, Lapitte) have sterile flowers but then produce minature plants or bulbils on the pole-likeinflorescence.


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Water lettuce, Pistiastratioites Bryophyllum sp. Agave sp.

Propagation

Artificial vegetative reproduction at its simplest involves inducing

stem cuttings to form roots by maintaining these in a humidenvironment. Treating the cuttings with a synthetic auxin such as

indole-3-butyric acid (typically diluted with inert talcum powder)

often speeds up the induction of adventitious roots. If cuttings donot readily root it may be necessary to use the technique of air-layering where rooting is induced on a branch still attached to the

parent plant. This involves removing a ring of bark, packing theexposed area with moist soil and keeping this sealed with plasticfilm until roots form, at which time the rooted cutting is removed

and planted. Some woody cuttings are very difficult to root. In suchcases, one must graft a bud (budding) or shoot cutting (grafting)

onto a root stock. Such vegetative propagation is necessary when anexact copy of the plant is desired. This is true for particular varieties

(more correctly cultivars) of woody plants like mango and hibiscus.

Since sexual reproduction leads to recombination, seed from suchplants will not produce offspring with identical traits to the parentand vegetative propagation is required.


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In plant tissue culture, sterileportions (explants) of a plant are

transferred to sterile mediumcontaining agar, mineral nutrients,

vitamins, sucrose and plant

hormones like auxins andcytokinins. This induces cells toreturn to a meristematic dividing

phase and produce a disorganisedproliferation of cells termed a

callus. By later changing theculture medium, calli can then be

induced to form shoots and rootsand so regenerate lots of tiny

plants. This technique canpropagate plants on an industrial

scale and has been used in theCaribbean for banana propagation.

It does require skilled personnel,specialised facilities and can take

a considerable time to regenerateplantlets and then to grow them to

a field-ready stage. It is also well-documented that genetic variation,

termed somaclonal variation, candevelop during the tissue cultureprocess so that the final plants

may not be identical. Thesetechniques ofin vitropropagation

are especially important for thegeneration of disease-free planting

material.


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plant nutrition is the study of the chemical elements that are necessary for growth

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