The effects of various intensity of UV-B on barley seedling were investigated by PS I and Ⅱ activities and chlorophyll fluorescence. The inhibitory effect of UV-B radiation on electron transport activity was increased as the intensity of UV-B irradiation was increased. Especially, PS Ⅱ is more sensitive to UV-B radiation than PS I is. By the addition of artificial electron donor, DPC, to the chloroplasts of the barley seedlings treated with UV-B, the photoreduction of DCPIP was recovered by only 11% on electron transport activity. However, the activity of PS Ⅱ was inhibited by 45% by the treatment with UV-B, but recovered it only 11% by the addition of DPC. These suggest that other sites besides the oxidation site of PS Ⅱ may be affected more by UV-B irradiation. As the intensity of UV-B was increased, Fo was increased while Fv was decreased, and thus Fv/Fm was decreased. This means that photochemical efficiency was reduced. With this parameters, it might be that UV-B radiation affected adversely to around PS Ⅱ.

Rice plants cv. Koshihikari, were subjected to the biologically effective ultraviolet-B (UV-B_BE) radiation {daily dose : 0.0 (control) and 11.5 (enhanced UV-B) kJ m^-2} to investigate the effect of enhanced UV-B radiation on lipid peroxidation and to determine whether carotenoids and polyamines are involved in protection mechanism against enhanced UV-B radiation. Enhanced UV-B radiation significantly depressed plant dry weight. Malondialdehyde (MDA) content in rice leaves was increased by about 30% after 6 days of UV-B irradiation. Total carotenoid contents tended to slightly decrease with the UV-B irradiation, even though there was no significance. In rice leaves, 3 major polyamines, putrescine, spermidine and spermine are observed. All of the polyamine contents were increased with UV-B irradiation. The results suggest that enhanced UV-B radiation caused oxidative stress on lipids and that polyamines may serve as a biochemical protectant against increased UV-B radiation in rice plants.