Biochemical aspects (antioxidants) for development of tolerance in plants growing at different low levels of ambient air pollutants.

The role of antioxidants, which are thought to scavenge the oxygen-free radicals in plants exposed to relatively low concentrations of ambient air pollutants for long durations, was studied for a year. Increases were observed in superoxide dismutase peroxidase activity, sulphate and leaf area to dry weight ratio, and decreases in stomatal conductance, ascorbic acid, protein content and total lipids, as a general response of all the plants in the polluted area. The results indicate that high peroxidase activity in the control plants and enhanced superoxide-dismutase activity in the polluted area might have enhanced the ability of Cassia siamea to tolerate stress better than Dalbergia sissoo. Similarly, enhanced activities in the polluted sites made Calotropis procera more tolerant of stress than Ipomoea fistulosa. Thus, it appears that monitoring of antioxidant activities offers a useful tool in understanding the mechanisms which make plants relatively tolerant in field conditions.