EFFECT OF SULFUR-DIOXIDE AND OZONE SINGLY OR IN COMBINATION ON LEAF CHLOROPHYLL, RNA, AND PROTEIN IN WHITE BEAN

The effect of 0.15 ppm ozone and (or) 0.15 ppm sulphur dioxide on leaf chlorophyll, RNA, and protein levels was investigated. Ozone-treated leaves exhibited reddish-brown colored lesions and an immediate and continuous decrease in chlorophyll a and b levels over a 5-day period, whereas protein levels increased and there was no effect of RNA levels compared to the control group of plants. Sulphur dioxide-treated leaves exhibited an immediate increase in chlorophyll a and b, but protein and RNA levels were not affected. The sulphur dioxide-ozone mixture caused an interveinal chlorosis by about day 3 and produced a decrease in chlorophyll a and b which was delayed by 2 days compared with leaves exposed to ozone alone. By the end of the 5-day period, chlorosis that occurred was not due to phaeophytinization of the chlorophyll molecules. Protein and RNA levels were not affected. Although both ozone and the pollutant mixture caused chlorophyll destruction and premature leaf drop, the changes that occurred in the leaf were not typical of normal leaf senescence.