2021-04-01 12:45:30
(a) Mottled chlorosis followed by the development of necrotic areas at the tips and margins of the leaves.
(b) K+ deficiency inhibits proteins synthesis and photosynthesis. At the same time, it increases the rate of respiration.
(c) The internodes become shorter and root system is adversely affected.
(6) Calcium
Calcium Deficiency in Leaves(i) Functions
(a) It is necessary for formation of middle lamella of plants where it occurs as calcium pectate.
(b) It is necessary for the growth of apical meristem and root hair formation.
(c) It acts as activator of several enzymes, e.g., ATPase, succinic dehydrogenase, adenylate kinase, etc.
(ii) Deficiency symptoms
(a) Ultimate death of meristems which are found in shoot, leaf and root tips.
(b) Chlorosis along the margins of young leaves, later on they become necrotic.
(c) Distortion in leaf shape.
(7) Magnesium
(i) Functions
(a) It is an important constituent of chlorophyll.
(b) It is present in the middle lamella in the form of magnesium pectate.
(c) It plays an important role in the metabolism of carbohydrates, lipids and phosphorus.
(ii) Deficiency symptoms
(a) Interveinal chlorosis followed by anthocyanin pigmentation, eventually necrotic spots appears 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.
(b) Stems become hard and woody, and turn yellowish green.
(c) Depression of internal phloem and extensive development of chlorenchyma.
Specific Role of Micronutrients
(1) Iron
Iron Deficiency(i) Functions
(a) Iron is a structural component of ferredoxin, flavoproteins, iron prophyrin proteins (Cytochromes, peroxidases, catalases, etc.)
(b) It plays important roles in energy conversion reactions of photosynthesis (phosphorylation) and respiration.
(c) It acts as activator of nitrate reductase and aconitase.
(ii) Deficiency symptoms
(a) Chlorosis particularly in younger leaves, the mature leaves remain unaffected.
(b) It inhibits chloroplast formation due to inhibition of protein synthesis.
(c) Stalks remain short and slender.
(2) Manganese
(i) Functions
(a) It acts as activator of enzymes of respiration (malic dehydrogenase and oxalosuccinic decarboxylase) and nitrogen metabolism (nitrite reductase).
(b) It is essential for the synthesis of chlorophyll.
(c) It is required in photosynthesis during photolysis of water.
(ii) Deficiency symptoms:
(a) Chlorosis (interveinal) and necrosis of leaves.
(b) Chloroplasts lose chlorophyll, turn yellow green, vacuolated and finally perish.
(c) Root system is poorly developed.
(d) Formation of grains is badly affected.
(3) Copper
(i) Functions
(a) It activates many enzymes and is a component of phenolases, ascorbic acid oxidase, tyrosinase, cytochrome oxidase.
(b) Copper is a constituent of plastocyanin, hence plays a role in photo-phosphorylation.
(c) It also maintains carbohydrate nitrogen balance.
(ii) Deficiency symptoms
(a) Both vegetative and reproductive growth are reduced.
(b) The most common symptoms of copper deficiency include 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.
(c) It also causes necrosis of the tip of the young leaves (e.g., Citrus). The disease is called 'die back'.
(4) Molybdenum
(i) Functions
(a) Its most important function is in nitrogen fixation because it is an activator of nitrate reductase.
(b) It is required for the synthesis of ascorbic acid.
(c) It acts as activator of some dehydrogenases and phosphatases.
(ii) Deficiency symptoms
(a) Mottled chlorosis is caused in the older leaves as in nitrogen deficiency, but unlike nitrogen-deficient plants, the cotyledons stay healthy and green.
(b) It is also known to inhibit flowering, if they develop, they fall before fruit setting.
(c) It leads to drop in concentration of ascorbic acid.
Notes on Mineral Nutrition
(5) Zinc
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