What is the plant’s minerals nutrition?
The roots of green plants absorb a large number of elements from the soil. Some of these elements are absolutely necessary for normal growth and development of the plant. The process involving the absorption and utilization of various mineral ions by plants for their growth and development is called minerals nutrition.
Essentiality of Elements for mineral nutrition
Plants may accumulate several elements which are not required by them and do not have any function. They are absorbed and accumulated by the plant simply because they are present in the soil. The essentiality of a mineral element for plant can be judged on the basis of the following measures:
i) The element must be absolutely essential for normal growth and development of the plant.
ii) The requirement of the element must be definite and it cannot be replaced by another element.
iii) The element must be directly involved in the nutrition of the plant, is a part of the structural molecule, and takes part in the biochemical process.
what are the role of minerals in plant nutrition?
An element can play three types of roles in a plant, such as: structural, electro-chemical and catalytic. Structural role includes its involvement in the formation of various components of the cell. Electro-chemical role involves balancing of ionic charges and stabilization of proteins and other macro- molecules. Catalytic role is its involvement as coenzyme or cofactor in enzyme reactions. Most of the micronutrients play catalytic role in minerals nutrition.
Macronutrient Elements for minerals nutrition
Nitrogen is taken by plants usually in the form of NO2- and NO3- from the soil. Most soils are deficient in nitrogen since this element is easily lost through discharge of nitrate ions or conversion of nitrate ions to volatile N2 by micro-organisms. . Nitrogen is essential to plants because it is a part of numerous organic compounds like amino acids, proteins, coenzymes, nucleic acids, vitamins, alkaloids and chlorophyll. It plays an significant role in protein synthesis, photosynthesis, respiration, growth and other metabolic processes.
Nitrogen deficiency symptoms include general yellowing (chlorosis), especially in mature leaves. Young leaves remain green longer because of soluble forms of nitrogen are transported to them from the older leaves. Plants grown in excess of nitrogen are usually dark green in color with thick foliage and poorly developed root system.
For minerals nutrition phosphorus, absorbed as a monovalent (H2PO4-) or divalent (HPO- -) phosphate ion, is transformed into organic form upon entry into the root or the shoot. It is a constituent of cell membranes, nucleic acids and nucleotides, certain coenzymes (NAD, NADP) and ATP. Its presence in sugar phosphates and coenzymes allows sugars to be metabolised by the plant. It also acts as an energy carrier. In growing plants, phosphorus is largely present in meristematic tissues as intense activity in these regions needs intense energy transformations. It also influences nitrogen metabolism in plants.
Deficiencies of phosphorus plants remain stunted and develop a characteristic dark blue-green or purple coloration and dead necrotic areas on various parts. Phosphorus deficiency seriously inhibits protein synthesis and sugars accumulate in vegetative parts. Maturity of phosphorus deficient plants is often delayed.
A large amount of potassium is required for proper growth and development of the plant. It acts as a coenzyme or activator for many enzymes. It helps in determining anion-cation balance and turgidity in cells and is intricate in protein synthesis. It is also involved in the creation of cell membranes and in opening and closing of stomata.
Sulphur a part of minerals nutrition is absorbed as SO4- - ions. Most of the absorbed sulphate is translocate as such to the shoot where it is incorporated into organic compounds like sulphur comprising amino acids. Since sulphur is a constituent of some amino acids, it has indirect role in protein synthesis. Sulphur deficiency indications to breakdown of protein synthesis. Sulphur deficient plants show general yellowing of leaves, first noticed in younger leaves.
Another part of minerals nutrition, Magnesium is present in the soil in water soluble, redeemable, and fixed forms. It plays important role in photosynthesis and carbohydrate metabolism. It is an essential part of chlorophyll molecule. Roots and micro-organisms which lack chlorophyll require magnesium for the activation of numerous essential enzymes. Those enzymes which are known to utilize energy in ATP are activated by magnesium. Magnesium deficiency tempts extensive inter-venial chlorosis and necrotic or purple spots on mature leaves.
Calcium in the soil happens in a non-exchangeable form. It is found in plants mostly inside cell vacuoles as crystals of calcium oxalate. In cell walls, calcium forms relatively insoluble salts by reacting with pectic acids in the middle lamella. . Calcium pectases of the middle lamella cement the primary walls together so that cells of a tissue remain bound to one another. Calcium performs an essential function in minerals nutrition for the synthesis and stability of pectic substances. In higher plants, calcium is needed in low concentrations in membranes to maintain its structure and characteristics of differential permeability. Mitotic divisions, organic acid metabolism and nitrogen metabolism are seriously disturbed due to calcium deficiency.
Iron is a relatively immobile ion and is absorbed both in ferrous and ferric forms. It has a number of important functions in the overall metabolism of plants. It is a vital constituent of ferredoxin and cytochromes and acts as an activator for enzymes catalyzing reactions of chlorophyll synthesis. Iron is also found in enzymes like peroxidases and catalases. Iron-deficient plants are causes lack of minerals nutrition and develop pronounced interveinal chlorosis on younger leaves.