Foliar injury and leaf diffusive resistance of rice and white bean in response to SO2 and O3, singly and in combination

Plants of rice (Oryza sativa) and white bean (Phaseolus vulgaris) were exposed to 524 microg m(-3) SO2, 392 microg m(-3) O3 and a mixture of both gases, i.e. 524 microg m(-3) SO2 and 392 microg m(-3) O3 to determine the visible foliar injury and leaf diffusive resistance. Response of leaf diffusive resistance was measured on upper and lower surfaces of leaves, i.e. the two unifoliate leaves of bean and the first, second and third primary leaves of rice. The difference in the response may be due to sensitive guard cells causing stomatal closure in the presence of O3, whilst a low concentration of SO2 caused the stomata to open. Thus, SO2 alone is known to decrease, and O3 tends to increase leaf diffusive resistance. However, exposure to both gases increases or decreases the resistance, depending on the species response.