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Functions – Mode of Absorption and Deficiency Symptoms of Macronutrients
Micronutrients even though required in trace amounts are essential for the metabolism of plants. They play key roles in many plants. Example: Boron is essential for translocation of sugars, molybdenum is involved in nitrogen metabolism and zinc is needed for biosynthesis of auxin. Here, we will study about the role of micro nutrients, their functions, their mode of absorption, deficiency symptoms and deficiency diseases.
1. Iron (Fe):
Iron is required lesser than macronutrient and larger than micronutrients, hence, it can be placed in any one of the groups. Iron is an essential element for the synthesis of chlorophyll and carotenoids. It is the component of cytochrome, ferredoxin, flavoprotein, formation of chlorophyll, porphyrin, activation of catalase, peroxidase enzymes.
It is absorbed as ferrous (Fe2+) and ferric (Fe3+) ions. Absorbtion of Fe2+ ions are comparitively more than Fe3+ ions. Mostly fruit trees are sensitive to iron.
Interveinal Chlorosis, formation of short and slender stalk and inhibition of chlorophyll formation.
2. Manganese (Mn):
Activator of carboxylases, oxidases, dehydrogenases and kinases, involved in splitting of water to liberate oxygen (photolysis). It is absorbed as manganous (Mn2+) ions.
Interveinal chlorosis, grey spot on oats leaves and poor root system.
3. Copper (Cu):
Constituent of plastocyanin, component of phenolases, tyrosinase, enzymes involved in redox reactions, synthesis of ascorbic acid, maintains carbohydrate and nitrogen balance, part of oxidase and cytochrome oxidase. It is absorbed as cupric (Cu2+) ions.
Die back of citrus, Reclamation disease of cereals and legumes, chlorosis, necrosis and Exanthema in Citrus.
4. Zinc (Zn):
Essential for the synthesis of Indole acetic acid (Auxin), activator of carboxylases, alcohol dehydrogenase, lactic dehydrogenase, glutamic acid dehydrogenase, carboxy peptidases and tryptophan synthetase. It is absorbed as Zn2+ ions.
Little leaf and mottle leaf due to deficiency of auxin, Inter veinal chlorosis, stunted growth, necrosis and Khaira disease of rice.
5. Boron (B):
Translocation of carbohydrates, uptake and utilisation of Ca++, pollen germination, nitrogen metabolism, fat metabolism, cell elongation and differentiation. It is absorbed as (borate) BO3- ions.
Death of root and shoot tips, premature fall of flowers and fruits, brown heart of beet root, internal cork of apple and fruit cracks.
6. Molybdenum (Mo):
Component of nitrogenase, nitrate reductase, involved in nitrogen metabolism, and nitrogen fixation. It is absorbed as molybdate (Mo2+) ions.
Chlorosis, necrosis, delayed flowering, retarded growth and whip tail disease of cauliflower.
7. Chlorine (Cl):
It is involved in Anion – Cation balance, cell division, photolysis of water. It is absorbed as Cl– ions.
Wilting of leaf tips.
8. Nickel (Ni):
Cofactor for enzyme urease and hydrogenase.
Necrosis of leaf tips.