Phytotoxicity of Air Pollutants

Abstract

Pisum sativum L. cv. Alsweet (garden pea) and Lycopersicon esculentum mutant flacca Mill. (tomato) were used to evaluate the phytotoxicity of SO2 and O3 in the light and dark. Plants were grown in controlled environment chambers and exposed to SO2 or O3 in the light or dark in the same environmental conditions under which they were grown. The pea plants were treated with fusicoccin to ensure open stomata in the dark; the stomata of the tomato mutant remained open in the dark. Both species exhibited 64% to 80% less foliar necrosis following exposure to SO2 (0.5-1.0 .mu.l/l for 2 h) in the light than in the dark. The decrease in SO2 injury for light versus dark exposed plants was greater in fully expanded than expanding leaves. Both species exhibited 30% greater foliar necrosis following exposure to O3 (0.2 .mu.l/l for 2 h) in the light than in the dark. The increase in O3 injury in the light versus dark was similar for leaves at all stages of expansion. Leaf conductance to water vapor was 7% to 11% and 23% higher in the light than in the dark for fusicoccin-treated peas and tomato plants, respectively, indicating greater foliar uptake of both pollutants in the light than in the dark. Thus, the decreased SO2 toxicity in the light was not associated with pollutant uptake, but rather with the metabolism of SO2. In contrast, the increased toxicity of O3 in the light was at least in part associated with increased uptake or could not be separated from it.