CELLULAR DETOXIFYING MECHANISMS DETERMINE THE AGE-DEPENDENT INJURY IN TROPICAL TREES EXPOSED TO SO2

The metabolic aspects responsible for the age dependent injury in two tropical tree species (Cassia siamea Lam. and Dalbergia sissoo Roxb.) exposed to SO2 were investigated. Plants of 6, 12, 24 and 48 months old were exposed to 96 mug m-3 SO2 for 6 h/day for 15 days and stomatal conductances, pollutant accumulation, sulphite turnover rate and antioxidants were measured. Results indicate that although conductances and accumulated sulphate were higher in C. siamea of different ages exposed to SO2 than those of D. sissoo, the cellular injury (MDA and soluble protein) was greater in D. sissoo. This was related to faster sulphite turnover rate, greatly enhanced peroxidase (POD) and superoxide dismutase (SOD) activities and ability to restore sufficient GSH levels via relatively unaffected GR activities in C siamea of 12, 24 and 48 months old, which were operating comparatively at a slower pace in 6 month old C siamea and D. sissoo of different ages. Thus, it was concluded that cellular detoxification mechanisms are age and species dependent and increase with the age of the plant.