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Organisms require many organic and inorganic substances to, complete their life cycle. All such substances which they take from, outside constitute their nutrition. On the basis of their nutritional, requirements, organisms can be classified into heterotrophs and, autotrophs., , All non-green plants and animals, including human beings,, are heterotrophs. Autotrophic green plants obtain their nutrition from, inorganic substances which are present in soil in the form of minerals,, ‘hich are known as mineral elements or mineral nutients and this, nutrition is called mineral nutition, , Essential mineral elements, , , , An essential element is defined as ‘one without which the plant, cannot complete its life cycle, or one that has a clear physiological, role’, Therefore, in 1939 Amon and Stout proposed the following, characters for judging the criteria of essentiality of an element in, the plant :, , (1) The element must be essential for normal growth and, reproduction, which cannot proceed without it, , (2) The requirement of the element must be specific and, cannot be replaced by another element,, , (3) The requirement must be direct that is, not the result of, any indirect effect e.g, for relieving toxicity caused by some other, substance., , , , Essential elements are divided into two broad categories,, based on the quantity in which they are required by plants. Macroelements and micro-elements, Their ionic forms are respectively, called macronutrients and micronutrients. Mineral salts dissolved in, soil solution are constantly passing downwards along with, percolating (gravitational) water. The phenomenon is called, leaching. Leaching is more in case of anions., , Mineral Nutrition, , Macronutrients (Macroelements or major elements) :, Which are required by plants in larger amounts (Generally present, in the plant tissues in concentrations of 1 to 10 mg per gram of dry, matter). Of the non-essential functional elements, silicon and, sodium often occur in the range of macroelements. Macroelements, are usually involved in the synthesis of organic molecules and, development of osmotic potential., , Micronutrients (Microelements or minor elements or, trace elements) : Which are required by plants in very small, amounts, Le., in traces (equal to or less than 0.1 mg per gram dry, matter). Cobalt, vanadium, aluminium and nickel, may be essential, for certain plants. Microelements are mostly involved in the, functioning of enzymes, as cofactors or metal activators. The usual, concentration of essential elements in higher plants according to, D.W, Rains (1976) based on the data of Stout are as follows, Table : 4., , "Bot dry weight, ‘Macrontirients, Carbon 45, Oxygen 45, Hydrogen 6, ‘Nitrogen 15, Potassium, Calcium, Magnesium, Phosphorus, Sulphur, , , , , , |, , Elements, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Chlorine, Tron, Manganese, Boron, , Zine, Copper, ‘Molybdenum

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628 Mineral Nutrition, , , , , , , , Plant analysis, , Ash analysis : The plant tissue is subjected to a very high, temperature (550-600°C) in an electric muffle furnace and is, reduced to ash, The plant ash left behind forms a very small, proportion of plants dry weight ranging from 2 to 10% only., Analysis of plant ash shows that about 92 mineral elements are, present in different plants. Out of these, 30 elements are present in, each and every plant and rest are in one or other plant. Out of, these 30 elements, 16 elements are necessary for plants and are, called essential elements., , Solution culture (Hydroponics) : In this method plants are, grown in nutrient solutions containing only desired elements. To, determine the essentiality of an element for a particular plant, it is, grown in a nutrient medium that lacks or is deficient in this, ‘element., , , , , , The growing of plants with their roots in dilute solutions of, mineral salts instead of soil led to increased understanding of plant, nutrition. This cultivation of plants by placing the roots in nutrient, solution is called hydroponics. Probably the first recorded use of, soilless culture was by Woodward in 1699, By 1860, the culture, solution technique was modemized by Sachs and he showed the, essentiality of nitrogen for plant growth,, , Another significant worker for studying the essentiality of, elements was Knop (1865). The method of growing plants in, aqueous nutrient solutions as employed by Sachs and Knop is, used experimentally and commercially today and known as, hydroponic culture. Now a days a chelating agent Na’-EDTA, (Disodium salt of ethylene diamine tetra acetic acid, EDTA, (Ethylene diamine tetra-acetic acid) is a buffer which is used in, tissue cultures is added., , Sand culture : Here plants are grown in inert sand +, nutrient solution. Main advantage is that roots get natural, environment and proper aeration., , Aeroponics : In this practice, plants are grown with their, roots bathed in nutrients mist. This method has been successfully, used in growing Citrus and olive., , Major role of nutrients, , Various elements perform the following major roles in the, plants, , Construction of the plant body : The elements particularly, ©, H and O construct the plant body by entering into the, constitution of cell wall and protoplasm. They are, therefore,, referred to as framework elements. Besides, these (C, H and O) N,, P and S, Mg and Fe also enter in the constitution of protoplasm., They are described as protoplasmic elements., , Maintenance of osmotic pressure : Various minerals, present in the cell sap in organic or inorganic form maintain the, osmotic pressure of the cell., , Maintenance of permeability of cytomembranes : The, minerals, particularly Ca**, K* and Na* maintain the permeability, of cytomembranes., , Influence the pH of the cell sap : Different cations and, anions influence on the pH of the cell sap., , Catalysis of biochemical reaction : Several elements, particularly Fe, Ca, Mg, Mn, Zn, Cu, Cl act as metallic catalyst, biochemical reactions,, , Toxic effects : Minerals like Cu, As, etc. impart toxic effect, cn the protoplasm under specific conditions,, , Balancing function : Some minerals or their salts act, against the harmful effect of the other nutrients, thus balancing, each other., , , , Specific role of macronutrients, , The role of different elements is described below, , (1) Carbon, hydrogen and oxygen : These three elements,, though can not be categorised as mineral elements, are, indispensible for plant growth. Carbon, hydrogen and oxygen, together constitute about 94% of the total dry weight of the plant., Carbon is obtained from the carbon dioxide present in the, atmosphere. It is essential for carbohydrate and fat synthesis., Hydrogen and oxygen would be obtained from water which is, absorbed by the plants from the soil. Some amount of oxygen is, also absorbed from the atmosphere., , (2) Nitrogen, , Source : The chief source of nitrogen for green plants is the, soil. It is absorbed mainly in the form of nitrate fons (NO}). The, major sources of nitrate for the plants are sodium nitrate,, potassium nitrate, ammonium nitrate and calcium nitrate., , Functions : Nitrogen is an essential constituent of proteins,, nucleic acids, vitamins and many other organic molecules as, chlorophyll. Nitrogen is also present in various hormones,, coenzymes and ATP etc. It plays an important role in protein, synthesis, respiration, growth and in almost all metabolic reactions., It also intensifies colouration in apple., , Deficiency symptoms, , (i) Impaired growth, Yellowing of leaves (appearing first in older leaves) due to, loss of chlorophyll, Le., chlorosis., , (ii) Development of anthocyanin pigmentation in veins,, sometimes in petioles and stems., , , , , , (iv) Delayed or complete suppression of flowering and fruiting., Excessive supply of nitrogen produces following symptoms :, (i) Increased formation of dark green leaves., , (ii) Poor development of root system., , , , ) Delayed flowering and seed formation., (3) Phosphorus, Source : Phosphorus is present in the soil in two general, forms, organic and inorganic. Organic compounds are decomposed, and phosphorus is made available to plants in inorganic form. Soil, solution contains phosphorus in inorganic forms as the phosphate, ions obtained as HPO; and HPO}-. When pH is low phosphate, , ions are present in the form of H,PO,. When pH is high,, Phosphate ions are represented in HPO}.

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Functions, , () Phosphorous is present abundantly in the growing and, storage organs such as fruits and seeds. It promotes healthy root, growth and fruit ripening by helping translocation of, carbohydrates., , (i) It is present in plasma membrane, nucleic acid,, nucleotides, many coenzymes and organic molecules as ATP., , , , (ii) Phosphorus plays an indispensable role in energy, metabolism i.e., hydrolysis of pyrophosphate. Thus itis required, for all phosphorylation reactions., , Deficiency symptoms, (i) Leaves become dark green or purplish., , (i) Sometimes development of anthocyanin pigmentation, ‘occurs in veins which may become necrotic (Necrosis is defined as, localised death of cells)., , (iii) Premature fall of leaves., , (iv) Decreased cambial activity resulting in poor development, of vascular bundles., , (v) Sickle leaf disease,, (4) Sulphur, Source : Sulphur is present as sulphate SO}- in, , fraction of soil. In industrialized areas, atmospheric sulphur dioxide, (SO,) and sulphur trioxide (SO, ; in low concentration) may be, , important sources of sulphur nutrition, , ral, , , , , , Functions, , (i) Sulphur is a constituent of amino-acids like cystine, cysteine, and methionine; vitamins like biotin and thiamine, and coenzyme A., , (ii) It increases the nodule formation in the roo!s of, leguminous plants. It favours soluble organic nitrogen and there is, decrease in the quantity of soluble nitrogen with its increase., (ii) The characteristic smell of mustard, onion and garlic is, due to the presence of sulphur in their volatile oils., , , , (iv) Sulphur in plants is required in stem and root tips and, ‘young leaves, It is remobilsed during senescence., , Deficiency symptoms, Leaves remain small and tum pale green i.e., symptoms of, chlorosis. Chlorosis affects young leaves more because of immobile, property of the sulphur. The young leaves develop orange, red or, purple pigment., , (i) Leaf tips and margins roll downwards and inwards eg.,, tobacco, tea and tomato,, , (ii) Delayed flowering and fruiting., , (iv) Apical growth is retarded whereas premature development, of lateral buds starts, , , , (v) The tea yellow disease is caused in tea plants., (vi) Decrease in stroma lamellae and increase in grana stacking., , (vii) Increase in starch and sucrose accumulation, and, decrease in reducing sugars., , Mineral Nutrition 629, (5) Potassium, , Source : Source of K* to the plants is inorganic compounds, like potassium sulphate, potassium nitrate, etc. Potassium is, usually present in sufficient amount in clay soils. It contains, approximately 0.3 to 6.0 percent of whole plant. In seeds,, found in less amount., , , , Functions, , (i) 1 differs from all other macronutrients in not being a, constituent of any metabolically important compound., , (ii) It is the only monovalent cation essential for the plants., , (il) It acts as an activator of several enzymes including DNA, polymerase., , (iv) It is essential for the translocation of photosynthates,, opening and closing of stomata, phosphorylation, synthesis of, nucleic acid and chlorophyll., , It takes part in the formation of cell membrane and it is also, responsible for maintenance of turgidity of cells., , Deficiency symptoms, , {i} Mottled chlorosis followed by the development of necrotic, areas at the tips and margins ofthe leaves., , (ii) K* deficiency inhibits proteins synthesis and photosynthesis., At the same time, it increases the rate of respiration., , (iii) The intemodes become shorter and root system is, adversely affected., , (iv) The colour of leaves may turn bluish green,, , (v) Widespread blackening or scorching of leaves may occur, asa result of increased tyrosinase activity., , (vi) Rosette or bushy habit of growth may be seen in plants., , Destruction of pith cells of tomato and increased, differentiation of phloem elements, , (6) Calcium, , Source : It is absorbed by the plants in the form of Ca*, from calcium carbonate etc. It occurs abundantly in a nonexchangeable form such as anorthite (CaAl,.Si,0,) . Much of the, exchangeable calcium of the soil is absorbed on to the surface of, clay micelle., , Functions, , , , (i) It is necessary for formation of middle lamella of plants, where it occurs as calcium pectate., , (i) It is necessary for the growth of apical meristem and root, hair formation,, , (iil) Ht acts as activator of several enzymes, e.g., ATPase,, succinic dehydrogenase, adenylate kinase, etc., , (iv) Along with Na* and Kt it maintains the permeability of, plasma membrane., , (v) It is involved in the organisation of spindle fibres during, mitosis,, , (vi) It antagonises the toxic effects of Na* and Mg'*., , It is essential for fat metabolism, carbohydrate metabolism,, nitrate assimilation and binding of nucleic acids with proteins

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630 Mineral Nutrition, , , , Deficiency symptoms, , (i) Ultimate death of meristems which are found in shoot, leaf, and root tips., along the margins of young leaves, later on they, , , , (ii) Distortion in leaf shape., (iv) Roots poorly developed or may become gelatinous., , (v) Young leaves show malformation and leaf tips becomes, hooked,, , (vi) Its deficiency checks flowering and causes the flowers to, fall early,, , (vii) Potato tubers become small and malformed,, , (7) Magnesium, , Source : Magnesium occurs in the soil in the form of, magnesite (MgCO,), dolomite (MgCO,, CaCO,), magnesium, sulphate (MgSO,) and as silicates. It is absorbed from the soil in, the form of (Exchangeable cation) ions (Mg**). It is easily leached, and thus become deficient in sandy soils during rainy season,, , Functions, , {i tis an important constituent of chlorophyll,, , (i) Tt 1 present in the middle lamella in the form of, magnesium pectate., , (ii) It plays an important role in the metabolism of, carbohydrates, lipids and phosphorus, , (iv) Itacts as activator of several enzymes,, , (v) Its required for binding the larger and smaller subunits of, ribosomes during protein synthesis., , Deficiency symptoms, , {i) Interveinal chlorosis followed by anthocyanin pigmentation,, eventually necrotic spots appear on the leaves. As magnesium is, easily transported within the plant body, the deficiency symptoms, first appear in the mature leaves followed by the younger leaves at, a later stage., , (i) Stems become hard and woody, and turn yellowish green., , (ii) Depression of intemal phloem and extensive development, of chlorenchyma,, Specific role of micronutrients, , (1) Iron, , Source ; It is present in the form of oxides in the soll, It is, absorbed by the plants in ferric ( Fe°* ) as well as ferrous (Fe*"), state but metabolically itis active in ferrous state. Its requirement is, intermediate between macro and micro-nutrients., , Functions, , (i) Iron is a structural component of ferredoxin, flavoproteins,, iron prophyrin proteins (Cytochromes, peroxidases, catalases, etc.), , (ii) It plays important roles in energy conversion reactions of, photosynthesis (phosphorylation) and respiration., , (ii) It acts as activator of ritrate reductase and aconitase., , (iv) Itis essential for the synthesis of chlorophyll, , Deficiency symptoms, , (i) Interveinal chlorosis particularly in younger leaves, the, mature leaves remain unaffected, , (ii) It inhibits chloroplast formation due to inhibition of protein, synthesis., , (iil) Stalks remain short and slender., (iv) Extensive interveinal white chlorosis in leaves., , (v) It may develop necrosis aerobic respi, affected., , , , severely, , (vi) In extreme deficiency scorching of leaf margins and tips, may occur., , (2) Manganese, , Source : Like iron, the oxide forms of manganese are, common in soil. However, manganese dioxide (highly oxidised, form) is not easily available to plants. It is absorbed from the soil in, bivalent form (Mn**), Oxidising bacteria in soils render manganese, unavailable to plants al pH ranging from 6.5 to 7.8., , Functions, , i) It acts as activator of enzymes of respiration (malic, dehydrogenase and oxalosuccinic decarboxylase) and nitrogen, ‘metabolism (nitrite reductase)., , (ii Itis required in photosynthesis during photolysis of water., , (ii) It decreases the solubility of iron by oxidation. Hence,, abundance of manganese can lead to iron deficiency in plants,, , , , Deficiency symptoms, (i) Chlorosis (interveinal) and necrosis of leaves., , (i) Chloroplasts lose chlorophyll, turn yellow green,, vacuolated and finally perish., , (ii) 'Grey speck disease’ in cat appears due to the deficiency, of manganese, which leads to total failure of crop., , (iv) (Marsh spots in seeds of pea., , (vy Deficiency symptoms develop in older leaves., , (3) Copper, , Source : Copper occurs in almost every type of soil in the, form of complex organic compounds. A very small amount of, copper is found dissolved in the soil solution. It is found in natural, deposits of chalcopyrite (CuFeS,)., , Functions, , , , It activates many enzymes and is a component of, phenolases, ascorbic acid oxidase, tyrosinase, cytochrome oxidase, , (i) Copper is a constituent of plastocyanin, hence plays a role, in photophosphorylation,, , (iii) It also maintains carbohydrate nitrogen balance,, , Deficiency symptoms, , (i) Both vegetative and reproductive growth are reduced., , (ii) The most common symptoms of copper deficiency indlude, a disease of fruit trees called ‘exanthema’ in which trees start, yielding gums on bark and ‘reclamation of crop plants’, found in, cereals and legumes., , (ii) It also causes necrosis of the tip of the young leaves (e.g., Citrus). The disease is called ‘die back’.

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(iv) Carbon dioxide absorption is decreased in copper, deficient trees., , {) Wiking of entire plant occurs under acute shortage., , (vi) Grain formation is more severely restricted than vegetative, growth,, , (4) Molybdenum, Source : It is available to the plants mostly as molybdate, is required in extremely small quantities by plants,, , Functions, , (i) Its most important function is in nitrogen fixation because it, is an activator of nitrate reductase., , (i) Its required for the synthesis of ascorbic acid., , (ii) It acts as activator of some dehydrogenases and, phosphatases., , Deficiency symptoms, , (i) Mottled chlorosis is caused in the older leaves as in nitrogen, Geficiency, but unlike nitrogen-deficient plants, the cotyledons stay, healthy and green., , Itis also known to inhibit flowering, if they develop, they, fall before fruit setting., (il) It leads to drop in concentration of ascorbic acid., , {iv) Its deficiency causes ‘whiptail disease’ in cauliflower and, cabbage. The leaves first show an interveinal mottling and the leaf, ‘margins may become gray and flaccid and finally brown,, , (5) Zine, , Source : Zinc occurs in the soll in the form of ferromagnesian, minerals like magnetite, biotite and homblende. Increase in soil pH, decreases the availability of zinc., , Bivalent form of zine (Zn**) is exchangeable and is readily, available in the soil. Plants requ this mineral only in traces and, its higher concentrations are highly toxic., , Functions, , (i) It is required for the synthesis of tryptophan which is a, precursor of indole acetic acid-an auxin,, , (ii) It is a constituent of enzymes like carbonic anhydrase,, hexokinase, alcohol dehydrogenase, lactic dehydrogenase and, carboxypeptidase,, , (ii) It is required for metabolism of phosphorus and, carbohydrates,, , (iv) Zine also appears to play an important role in protein, synthesis because in its absence there is substantial increase in, soluble nitrogenous compounds., , Deficiency symptoms, , (i) The first symptom appears in the form of interveinal, chlorosis of the older leaves, starting atthe tips and the margins., , (ii) Growth becomes stunted due to formation of smaller, leaves and shortened internodes. Reduced stem growth is due to, less synthesis of auxin., , (i) The leaves become distorted and sickle shaped and get, clustered to form rosettes. This effect is known as little leaf disease’., , (iv) In maize, zinc deficiency produces ‘white bud disease’, which leads to greatly reduced flowering and fruiting as well as, poorly differentiated root growth., , , , , , ions., , , , , , , , , , Mineral Nutrition 631, , (©) Its deficiency causes khaira disease of rice and mottled leaf, of apple, Citrus and walnut., , (6) Boron, , Source : Boron is present in the soil in very small amounts. It, appears in exchangeable soluble and nonexchangeable forms in the, soil BO} or B,O}. It is absorbed from the soil as boric acid, {HBO,) and tetraborate anions,, , Functions, , (i) It facilitates the translocation of sugars., , (ii) Itis involved in the formation of pectin., , (iii) It is also required for flowering, fruiting, photosynthesis, and nitrogen metabolism,, , (iv) Boron is required for uptake and utilisation of Ca**, pollen, germination, seed germination and cell differentiation., , (w) It regulates cellular differentiation and development., , Deficiency symptoms, , (i) The first major symptom of boron deficiency is the death of, shoot tip because boron is needed for DNA synthesis., , (ii) Generally flowers are not formed and the root growth is, stunted., , (ii) The leaves develop a thick coppery texture, they curve, and become brittle., , (iv) Some of the physiological diseases caused due to boron, deficiency are internal cork of apple, top rot of tobacco, cracked, stem of celery, browning of cauliflower, water core of turnip, hard, fruit of Citrus and heart rot of sugar beets and marigold. These, diseases can be cured by application of small doses of sodium, tetraborate in the soil, , (v) Its deficiency checks the cell division of cambium but, continues cell elongation,, , (7) Chlorine, , Source : It is absorbed from the soll as chloride ions. Hence,, it is rarely supplied as fertilizer., , Functions:, , {i) It is required for photolysis of water during photosynthesis, in photosystem-Il., , {ii) In tobacco, it increases water volume inside the cell and, also regulates carbohydrate metabolism,, , (ii) With Na* and K*, chlorine helps in determining solute, concentration and anion cation balance in the cells., , (iv) Itis essential for oxygen evolution in photosynthesis,, , Deficiency symptoms, , () The deficiency symptoms of chlorine consist of wilted, leaves which later become chlorotic and finally attain a bronze, colour,, , (i) Roots become stunted or thickened and club shaped and, fruiting is reduced., , (ii) Photosynthesis is also inhibited, , Critical elements : Macroelements which become, commonly deficient in the soils are called critical elements, They, are in number-N, P and K most ferilsers contain critical elements., They are called complete fertilisers.