EFFECT OF ZN2-SATIVA CV MANHAR) ON GROWTH AND PHOTOSYNTHETIC PROCESSES( STRESS IN RICE (ORYZA)

Effect of three Zn2+ concentrations, i.e. 0.075 (cl), 7.50 (c2) and 37 .5 (c3) mu M, on rice seedlings was studied at three stages, i.e. 7, 1 4 and 21 d after transplantation. Typical deficiency symptoms were obs erved in both solution and sand cultures of c1 and c2, but the effects were more pronounced in the solution culture. The c3 concentration wa s toxic. There was marked reduction in growth, chlorophyll (Chi) conte nts (particularly Chi b), Hill reaction activity, photophosphorylation rate (particularly non-cyclic photophosphorylation), thylakoid phosph orylation, and (CO2)-C-14-fixation at the cl concentration. However, a similar reduction was also observed in thylakoid phosphorylation at t he c3 concentration. Hence the optimum zinc concentration in the nutri ent medium lied between c2 and c3 Zn2+. By regression the theoretical optimum Zn concentration was calculated as 19.20 mu M (1.28 mg kg(-1)) Zn2+. Partitioning of C-14-photosynthates indicated reduced C-14 allo cation to sugar and starch fractions and increased free amino acids co ncentration at the cl concentration and vice-versa at c2 and c3.