Functions of Zn :- Visual symptoms :- Predisposing factors:- Corrective measures :- Zinc is predominantly taken up as a divalent cation (Zn2+). In plants, zinc is not oxidized or reduced but acts either as metal component of the enzymes or as functional, structural, or regulatory cofactor of large number of enzymes like alcohol dehydrogenase, superoxide dismutase (SOD), carbonic anhydrase and RNA polymerase. Zinc deficiency is associated with an impairment of carbohydrate metabolism and protein synthesis. Distinct zinc deficiency symptoms of stunted growth and ‘little leaf ’ are related to disturbances in the metabolism of IAA. High IAA oxidase activity is considered to be responsible for low IAA levels. Zinc translocation from roots to shoots is inhibited by phosphorus and physiological inactivation of zinc within the shoots also occurs. Zinc affects phosphorus metabolism in roots and increases the permeability of the plasma membranes of root cells to phosphorus and chlorine. Zinc protects bio-membrane integrity through protective role of SOD enzymes against lipid peroxidation. With zinc deficiency, phosphorus toxicity symptoms appear and P content may reach greater than 2.0% leaf dry weight. The characteristic visible symptoms of zinc deficiency are stunted growth (shortening of internodes) and a drastic decrease in leaf size, which combines with chlorosis. Decreased internodal length was a common symptom of Zn deficiency. Lower leaves first show a slight loss of colour at the tips and margins and this was followed by development of white spots on the leaves. Zinc deficiency occurs when available zinc content in the soil is low. High Phosphorus in the soil also induces zinc deficiency. It occurs in calcareous soils of high pH. Cool temperatures and wet spring seasons bring about the onset of zn deficiency due to restricted root growth. Corrective measures for Zn deficiency are preventive soil application or foliar application of elemental zinc or Zn salts.

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