Functions of Cu :- Visual symptoms :- Predisposing factors:- Corrective measures :- The divalent copper ion (Cu2+) is complexed to low molecular weight organic compounds. Enzymatically bound copper participates in redox reactions and the terminal oxidation in living cells is catalysed by iron. Copper is present in plastocyanin, peroxidases and oxidases. In copper deficient plants activity of these enzymes decreases rapidly. In chloroplasts, more than 50% of the copper is bound to plastocyanin and the rate of photosynthesis also gets affected with copper deficiency. Plants with copper deficiency contain lower amount of soluble carbohydrates during vegetative phase, lignification is impaired and this leads to distortion of young leaves, bending and twisting of stems. Lignification in copper deficient plants is inhibited because of lower phenolase activity, which oxidizes p-coumaric acid, one of the precursors of lignin biosynthesis. In copper deficient plants lignificatin of anther cell walls is reduced and microsporogenesis and pollen formation gets affected. Critical level of copper for copper deficiency is 3-5 mg/g dry wt. Chlorosis due to copper toxicity can also be a direct result of the action of high copper concentrations on lipid peroxidation and thus the destruction of the thylakoid membranes. Increase in nicotine content and the decrease in ascorbic acid oxidase activity is commonly observed in Cu deficient leaves. Cu deficiency results in stunted growth, distortion and bleaching of young leaves and it lead to cell death and necrosis. A higher dose of copper inhibited root growth before shoot growth is affected and this results in chlorosis. Cu deficiency is very rare in tobacco. It occurs when soils are poor in available Cu concentration in soil solution is governed by copper adsorption to soil particles. Foliar application of copper in the form of inorganic salts, oxides or chealates is required to correct copper deficiency rapidly in tobacco field crop.

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