Effects of UVB radiation on protein turnover of Rubisco and LHCII in rice

摘要

Ultraviolet-B (UV-B) radiation can damage plants, decreasing biomass and productivity. We previously found that rice cultivars vary widely in the sensitivity to supplemental UV-B radiation in 198 rice cultivars that belonged to five Asian rice ecotypes from the Bengal region, Indonesia and Japanese lowlands and uplands (Sato & Kumagai 1993). Among Japanese lowland rice, the 'Sasanishiki' cultivar (one of the leading cultivars in the northern part of Japan) was more resistant to the inhibitory effects of supplemental UV-B radiation on growth than the Norin 1 cultivar, although these cultivars are closely related (Kumagai & Sato 1992; Hidema et al. 1996). It has been reported that the supplemental UV-B radiation causes reduction in the amounts of chlorophyll (Chl), and ribulose-1, 5-biphosphate carboxylase/oxygenase (Rubisco) in leaves of C3 plants (Strid et al. 1990). On the other hand, it has also been shown that the level of Rubisco in leaves changed dramatically with leaf age, and that the levels of leaf proteins in rice are balanced by synthesis and degradation throughout the leaf life (Mae et al., 1983). In this connection, we found that supplemental UV-B radiation resulted in the reduction in the amounts of total leaf nitrogen, Chl, and Rubisco in fully expanded leaf in rice (Hidema et al. 1996). It was especially noticed that the amount of Rubisco was remarkably decreased by supplemental UV-B radiation in an UVsensitive Norin 1. This was not the case in an UV-resistant Sasanishiki. In this experiment, we investigated the effects of supplement UV-B radiation on the synthesis and degradation of Rubisco and LHCII with leaf age using ~(15)N tracer and the changes in the mRNA levels for rbcS, rbcL, and cab, and the cultivar difference betweenSasanishiki and Norin 1 cultivars in the sensitivities to the effects of supplemental UV-B on those biosyntheses.