Abstract
Three rice cultivars, Koshihikari, Suwon 258 and IR 74, were grown in environmentally-controlled glass chambers with three levels of biologically effective ultraviolet-B (UV-BBE) radiation [daily dose : 0.0 (No UV-B), 6.5 (Low UV-B) and 11.3 (High UV-B) kJm-2, UV-BBE] for 4 weeks of the early growth period. UV-B radiation significantly depressed plant dry weight and height in different extent among the cultivars. Suwon 258 was relatively less sensitive and IR 74 was most susceptible to UV-B with Koshihikari being between the two cultivars. Leaf area of all the cultivars was reduced by UV-B. Specific leaf weight, index of leaf thickness, of Suwon 258 was significantly increased by UV-B, while that of Koshihikari and IR 74 did not change significantly. Total chlorophyll content of Koshihikari and IR 74 was de creased, but that of Suwon 258 was not affected. Amount of UV-absorbing compounds on leaf area basis was increased for all the cultivars with both Low and High UV-B treatments. In Suwon 258 and IR 74, more negative natural abundance of 13C (δ13C) was observed with high UV-B treatment. These results indicate that rice plants may be affected by UV-B radiation in the amount of present-day sunlight and that intraspecific variation in the leaf thickenss response may primarily contribute to the differences among the cultivars in susceptibility to UV-B enhancement.
