Functions of Mn :- Visual symptoms :- Predisposing factors:- Corrective measures :- Manganese is absorbed mainly as Mn2+ and is translocated predominantly as the divalent cation in the xylem from the roots to the shoot. Manganese can replace Mg2+ in many reactions for example in its role as a bridge between ATP and enzyme complexes. The most well known function of manganese is its involvement in photosynthetic O2 evolution. Rate of photosynthesis declines and progressive disorganization of the lamellar system of the chloroplasts also occurs. Manganese containing SOD protects the tissues from the deleterious effects of oxygen free radical. Tobacco plant requires Mn for its normal growth, but it is sensitive to toxicity. The manganese deficiency begins with a light chlorosis of the young leaves and netted veins of the mature leaves especially when they are viewed through transmitted light. Chlorosis usually takes place only between the veins and follows outward to the minutest branches of the vascular system, resulting in a checkered appearance of the tobacco leaf. Small chlorotic symptoms developed on the leaves at later stages. Manganese deficiency affects cell elongation more than cell division and formation of lateral roots ceases completely. Intercostal chlorosis of the younger leaves is the most distinct symptom of manganese deficiency. Manganese induces magnesium deficiency and competition occurs between these two elements for binding sites in the roots during uptake as well as various metabolic reactions. Mn2+ not only competes effectively but also in some way blocks the binding sites for Mg2+. Poorly drained soils, high organic matter and high pH are some of the causes of Manganese deficiency Mn deficiency can be corrected by foliar/soil application of elemental manganese or chelated salts of manganese.

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