EFFECT OF ZINC ON FREE-RADICALS AND PROLINE IN BRASSICA AND CAJANUS

Investigations were carried out to study the effect of zinc on growth, free radical production and proline accumulation in shoots of Brassica juncea (Brassicaceae) and Cajanus cajan (Fabaceae). Seedlings were raised in modified B-5 medium supplemented with zinc sulphate under controlled aseptic conditions. In general, small concentrations of zinc (up to 0.1 mM) promoted growth of seedlings in both plant species. In contrast, production of free radicals (measured in terms of malondialdehyde) and the level of proline were low in the seedlings raised in the presence of these concentrations of zinc. However, zinc at higher concentrations significantly reduced growth, but promoted generation of free radicals as well as the accumulation of proline. Irrespective of the concentration of zinc sulphate, the shoots of C. cajan showed significantly higher levels of malondialdehyde as well as proline as compared with those of B. juncea. These results suggest the existence of a correlation between,the generation of free radicals and the accumulation of proline. In this communication we propose that accumulation of proline is related to non enzymatic detoxification of free radicals that are generated excessively under stress.