DIFFERENTIAL RESPONSE AND DETOXIFYING MECHANISMS OF CASSIA-SIAMEA LAM. AND DALBERGIA-SISSOO ROXB. OF DIFFERENT AGES TO SO2 TREATMENT

Seedlings of Cassia siamea Lam. and Dalbergia sissoo Roxb. of differen t ages (6 months, 1, 2 and 4 years old) were given SO2 treatment (appr oximately 55 +/- 5 mu g/m(3)) in 1 x 1 x 1 m(3) open top polythene cha mbers for 44 days (8 hours daily) in the experimental fields of black cotton soil. On 45th day, composite leaf samples were analysed for sto matal conductances, protein content, nitrate reductase activity (NRA), superoxide dismutase (SOD) activity, peroxidase (POD) activity, and a scorbic acid content. Stomatal conductances, sulphate content, POD and SOD increased while, protein content, NRA and ascorbic acid content d ecreased in both C. Siamea and D. sissoo. In both cases, the plants wi th advancement of age develop the detoxifying machanisms by the enhanc ement in antioxidant production under SO2 stress and thus, the SO2 tox icity decreased in the plants of higher age. Further, C. siamea of 1, 2 and 4 years old possess the ability to enhance POD and SOD activitie s, and to lower reductions in ascorbic acid content than that of D. si ssoo and thus, would have resulted in less cellular injury.