DIFFERENCES IN THE SENSITIVITY TO UVB RADIATION OF 2 CULTIVARS OF RICE (ORYZA-SATIVA L)

The effects of UVB radiation on the growth of two cultivars of Japanes e lowland rice (Oryza sativa L.), Sasanishiki and Norin 1, were examin ed in a phytotron. Supplementation of visible radiation with UVB radia tion reduced plant length, tiller number, the fresh and dry weights of the aboveground parts of plants, and the amounts of total leaf nitrog en, chlorophyll, soluble protein and ribulose-1,5-bisphosphate carboxy lase/oxygenase (Rubisco) in the eighth leaf, the youngest fully expand ed leaf. By contrast, UVB radiation significantly increased the accumu lation of UV-absorbing compounds, There was a difference between the t wo cultivars in the resistance to the effects of UVB radiation, The re duction in the amounts of Rubisco was smaller in Sasanishiki, while th e increase in the accumulation of UV-absorbing compounds was greater i n Sasanishiki. Parameters of plant growth, with the exception of the a mount of Rubisco, decreased in direct proportion to decreases in total leaf nitrogen in plants grown under lower or higher doses of UVB radi ation. However, the decrease in the Rubisco content of Norin 1 grown u nder a high dose of UVB radiation was exceptionally marked, and was no t observed similarly in Sasanishiki. These results suggest that the re markable reduction in Rubisco content in Norin 1 might have been due t o the specific effects of UVB radiation. It is also suggested that the difference between cultivars in the resistance to UVB radiation might be due to the differences in the levels of Rubisco and in UV-absorbin g compounds that are induced by UVB radiation.