INFLUENCE OF EXPOSURE TEMPERATURE AND RELATIVE HUMIDITY ON THE RESPONSE OF PINTO BEAN FOLIAGE TO SULFUR-DIOXIDE

When 20-day-old pinto bean plants (Phaseolus vulgaris 'Pinto III') were exposed to 0.9 ppm sulfur dioxide (SO2) the amount of trifoliolate leaf injury induced by SO2 generally was greater at 32C than at either 13 or 21 C, and greater at 80% relative humidity (RH) than at 40 and 60% RH. However, injury was less following exposures at 32 C for 1 hr and 21 C for 1 and 2 hr than that caused by equivalent exposures at 13 C. Stomatal conductance increased significantly with increased temperature and RH. Stomatal conductance of trifoliolates leaves from plants exposed to SO2 was less than that of exposed control plants. The foliar content of SO2, evaluated after exposures at 21 and 32 C, generally was greater at the higher temperatures.