1997. Response of oxidative stress defense systems in rice {Oryza sativa) leaves with supplemental UV-B radiation. -Physiol. Plant. 101: 301-308.The impact of elevated ultraviolet-B radiation (UV-B, 280-320 nm) on membrane systems and lipid peroxidation, and possible involvement of active oxygen radicals was investigated in leaves of two UV-B susceptible rice cultivars {Oryza sativa L. cvs IR74 and Dular). Rice seedlings were grown in a greenhouse for 10 days and then treated with biologically effective UV-B (UV-BBE) radiation for 28 days. Oxidative stress effects were evaluated by measuring superoxide anion (OD generation rate, hydrogen peroxide (H2O2) content, malondialdehyde (MDA) concentration and relative electrolyte conductivity (EC) for IR74 and Dular at 0 (control), 6 or 13 kJ m"" day"' UV-BBE-Significant increases in these parameters were found in rice plants grown at 13 vs 0 kJ m^" day"' UV-BBE after 28 days; indicating that disruption of membrane systems may be an eventual reason for UV-B-induced injury in rice plants. There was a positive correlation between O2" generation and increases in EC or MDA in leaves. Activities of enzymatic and nonenzymatic free radical scavengers were measured for IR74 after 7, 14, 21 and 28 days of exposure to 13 or 0 UV-BBE to evaluate dynamics of these responses over time. Activities of catalase and superoxide dismutase (but not ascorbate peroxidase) and concentrations of ascorbic acid and glutathione were enhanced by 13 vs 0 UV-BBE after 14 days of UV-B exposure. Further exposure to 28 days of UV-B was associated with a decline in enzyme activities and ascorbic acid, but not glutathione. It is suggested that UV-B-induced injury may be associated with disturbance of active oxygen metabolism through the destruction and alteration of both enzymatic and nonenzymatic defense systems in rice.

Twenty‐two cultivars of rice (Oryza sativa L.) from diverse origins were grown under greenhouse conditions and exposed to ultraviolet‐B radiation (UV‐B; 280‐320 nm) simulating a 5% reduction in stratospheric ozone in spring for the Philippines (14° N lat.) to evaluate growth and morphological responses to UV‐B. In comparison to controls that received no UV‐B, plants exposed to UV‐B exhibited significantly reduced dry matter production (total plant and shoot), shoot height, leaf blade length and total leaf area, increased number of tillers, and greater weight fractions in leaf blades and roots. For most cultivars, the relative effects of UV‐B on shoot morphology were greater than the effects on biomass production. The direction of the UV‐B effects were generally similar for all cultivars, however, there were significant differences among cultivars in the magnitude of the UV‐Binduced changes. Upland cultivars (IRAT104 and OS4) and two lowland cultivars commonly planted in the USA (Star Bonnet and Lemont) were found to be least affected by the UV‐B, whereas modern, high yielding, lowland cultivars developed in the Philippines (IR52, IR35546‐17‐33, and IR58) were found to be among the most sensitive to UV‐B. Our results indicate that in rice, as in other grasses, shoot morphology may be more responsive to solar UV‐B change than plant productivity. Intraspecific variation in morphological responses to UVB could contribute to differences among cultivars in susceptibility to UV‐B‐induced changes in competitive balance between rice and associated weeds of the rice agroecosystem.

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The survival of rice seedlings (Oryza sativa L.) after complete Submergence in water decreased with increased duration of submergence; with increased depth, temperature, and turbidity of water; and with increased rates of N fertilization. Survival increased with high light intensity and plant carbohydrate content. Factors that influence the survival of submerged plants also determine the amounts of N and carbohydrate in the plant.