Role of Mineral Elements in Plant Nutrition
The major roles and deficiency symptoms of mineral elements in the plants are as follows:
Nitrogen is absorbed mainly in the form of nitrate ions.
Major roles: It is a structural component of amino acid, nitrogenous bases, nucleic acid etc. Nitrogen is also present in the porphyrin structure of chlorophyll, cytochrome enzymes and some plant hormones. Nitrogen is essential for protein synthesis, cell division, growth, photosynthesis and metabolic activities
Deficiency symptoms: Chlorosis is the main symptom of nitrogen deficiency. The leaves gradually become pale and yellow. The symptom first appears in old leaves and later in the young leaves. Another characteristic symptom of nitrogen deficiency is the development of anthocyanin in stems, leaf veins and petioles which show red and purple streaks or patches. Other effects include suppressed shoot growth, sparse foliage, thin and weak stems, early defoliation and suppression of flowering and fruiting.
The plants obtain phosphorus in the form of soluble phosphate. . The maximum accumulation of phosphorus is found in rapidly growing region such as meristematic region and maturing fruits and seeds.
Major roles: Phosphorus is an important constituent of plant protein, phospholipids, sugar phosphate, nucleic acid, ATP and NADP.
Deficiency symptoms: Plants become stunted and older leaves fall down. Anthocyanin pigments develop in the leaves and leaf veins. In extreme cases, necrotic areas develop on leaves, petioles and fruits. A characteristic feature of phosphorus deficiency is the tremendous increase in the activity of the enzyme, phosphatase. Premature abscission, delayed flowering, premature fall of flower buds, poor vascular tissues and delayed seed germination are all the symptoms of phosphorus deficiency.
Potassium is present in the soil as water soluble in organic salts such as potassium sulphate, potassium phosphate, potassium nitrate etc. It is absorbed from the soil in the form of potassium ions.
Major roles: It acts as an activator in protein metabolism and it is also needed for DNA polymerase. It is also required in the synthesis and translocation of carbohydrates, cell division, development of chlorophyll, photosynthesis, respiration, protein synthesis, maintenance of cell turgidity, stomatal movements and reduction of nitrates. It also controls cellular organisation, hydration and permeability.
Deficiency symptoms: Potassium deficiency usually begins with a characteristic mottled chlorosis of older leaves that gradually spreads to younger leaves. The plants show rosette or bushy habit of growth due to loss of apical dominance. The stem becomes weak and the resistance of plants to pathogens is lowered. Consequently, the plants are easily lodged and attacked by diseases.
It occurs abundantly in non-exchangeable form such as anorthite. Calcium is one of the constituents of the middle lamella of the cell wall. There, it occurs as calcium pectate
Major roles. It affects the permeability of cytoplasmic membrane. It also plays an important role in lipid metabolism, cell division and cell enlargement. Calcium combines with organic acid into insoluble calcium oxalate which does not injure protoplasm. It favours translocation of carbohydrates and amino acids. It encourages root development.
Deficiency symptoms. Young leaves show malformation and the leaf tip becomes hooked. Calcium deficiency results in stunted growth, degeneration of meristems, chlorosis and necrosis. checks flowering and causes the flowers to fall early.
Sulphur is absorbed by plants as sulphate ions.
Major roles: Sulphur is a constituent of amino acids like cystine, cysteine and methionine, vitamins like biotin and thiamine and coenzyme A. Sulphur is also a constituent of ferredoxin and some of the lipids present in chloroplast. The sulphydryl group reduces the action of growth inhibitors and poisons by binding with them. It helps in chlorophyll formation, growth metabolism and nodule formation in legumes.
Deficiency symptoms: Sulphur deficiency causes chlorosis in young leaves, stunted growth, accumulation of anthocyanins, leaf curl, less juice contents in citrus, reduced nodulation in legumes
Magnesium occurs in the soil in the form of magnesite, dolomite, magnesium sulphate and as silicates. It is absorbed from the soil in the form of ions (Mg++).
Major roles: It helps in chlorophyll formation, growth, metabolism, and nodule formation in legumes. Enzymes involved in carbohydrate metabolism require magnesium as an activator. It also serves as activator for enzymes involved in the synthesis of nucleic acids
Deficiency symptoms: Magnesium deficiency causes interveinal chlorosis with purple anthocyanin pigmentation appearing first in the older leaves, marginal curling, premature leaf abscission, reduced growth, underdeveloped phloem and pith.
It occurs in the soil in the form of oxides and hydroxides. It is absorbed as ferric ions.
Major roles: It plays an important role in energy conversion reactions of photosynthesis and respiration. It is essential for the synthesis of chlorophyll and synthesis of protein.
Deficiency symptoms: Deficiency results in interveinal chlorosis. In extreme deficiency, scorching of leaf margins and tips may occur.
Manganese occurs in the soil in various forms (example, bivalent, trivalent and tetravalent) but is absorbed largely in manganous form (Mn++).
Major roles: Manganese activates enzymes of respiration, photosynthesis and nitrogen metabolism performing oxidation, reduction, decarboxylation and photolysis.
Deficiency symptoms: Deficiency results in marsh spot disease, interveinal chlorosis and necrosis in old leaves.
It is available to the plants mostly as molybdate.
Major roles: It plays an important role in the fixation and assimilation of nitrogen. It acts as an activator for nitrate reductase enzyme.
Deficiency symptoms: Deficiency causes, mottled chlorosis with marginal necrosis, whiptail disease in cabbage and loosening of inflorescence in cauliflower.
It is absorbed from the soil as boric acid and tetraborate anions.
Major roles: It helps in the absorption and translocation of carbohydrates, active salt absorption, cell division, pollen germination, synthesis of pectins, proteins and nucleic acid.
Deficiency symptoms: Death of root and shoot tips, loss of apical dominance, stunted growth, small size of fruits, and rosetting of leaves. Diseases caused by boron deficiency are internal cork of apple, rot of tobacco, cracked stem of celery, browning of cauliflower, heart rot of sugar beets.
Plants absorb divalent form of copper (Cu++) from the soil.
Major roles: It is a part of plastocyanin which acts as an electron carrier in photosynthetic reaction.
Deficiency symptoms: Diseases caused due to copper deficiency are exanthema, reclamation of crop plants, die back disease, and blackening of potato tubers.
Bivalent form of zinc is readily available in the soil.
Major roles: Zinc is essential for the synthesis of tryptophan and protein synthesis. It is an activator of several enzymes.
Deficiency symptoms: Leaf malformations, leaf rosettes, interveinal chlorosis, and stunted growth. The diseases are little leaf disease and white bud disease.
It is absorbed from the soil as chloride ions.
Major roles: It acts as an enzyme activator and stimulates photosynthesis.
Deficiency symptoms: Deficiency symptoms include leaf wilting, chlorosis, necrosis, swollen root tips, flower abscission and reduced fruiting.