EFFECTS OF UVB RADIATION ON STOMATAL DENSITY AND OPENING IN RICE (ORYZA-SATIVA L)

Ultraviolet-B (UVB, wavelength 280-320 nm) radiation has been demonstrated to affect growth and development of many plants. This study was conducted to determine the effect of UVB radiation on stomatal density and opening of Oryza sativa and to test if the stomatal response to UVB was associated with different sensitivity of growth to UVB in four cultivars. Ten-day-old seedlings of IR45 and IR74 (UVB sensitive), and IR64 and IR30 (UVB less sensitive), were subjected to UVB radiation in a glasshouse for 6 h d(-1) for 4 weeks. The unweighted UVB radiation was 1.94 W m(-2) for UVB treatment and 0.15 W m(-2) for control. Leaf area and plant dry mass were determined every 2 weeks while stomatal density and opening were recorded weekly. Results showed that a 2-week UVB treatment had no effect on the leaf area or plant dry mass of any test cultivar, but significantly reduced stomatal density and opening in IR45 and IR74. Under 4-week UVB exposure, leaf area and plant dry mass of IR45 and IR74 were significantly reduced. Stomatal density decreased in all cultivars, except in IR64. Greater reduction of stomata on the adaxial surface than on the abaxial surface under 3 and 4 weeks of UVB exposure suggests a direct effect of UVB radiation on stomata. IR45 and IR74 showed significant reductions in stomatal opening after 2 weeks of exposure to UVB, while stomatal opening in IR30 and IR64 decreased significantly after only 4 weeks of UVB treatment. Difference in plant dry mass between UVB treated and control plants was significantly correlated with the reductions in stomatal opening and density on adaxial surface under UVB treatment. Thus, reduction in dry mass of rice plants under UVB in the glasshouse could be attributed to decrease in stomatal density and opening. (C) 1995 Annals of Botany Company