Resistance of rice to ultraviolet-B radiation based on UVB-induced DNA lesions and their photorepairs

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1 Changes in DNA lesions during growth in rice: (1) We found that rice could be more susceptible to CPD induction at the stage when the second, third or fourth leaves are developing, and UVB sensitivity correlates with low CPD photorepair. (2) Dark-grown etiolated rice does not have any CPD photorepair ability, and the induction of CPD photorepair was shown to be controlled by phytochrome/cryptochrome photosystems. (3) It was evident that 2-3 CPDs/Mb. DNA is always being kept in rice growing in solar radiation.2 Cultivar differences in CPD photorepair between UV-resistant and -sensitive rice : We previously suggested that two possibilities might account for CPD photorepair defiviency in UV-sensitive rice (Norin 1). One is due to a structural mutation, which could affect the formation of CPD-photolyase complex, or dissociation of the complex. The other is due to mutation of regulatory mechanisms for induction of photolyase, which could decrease the levels of photolyase. Based on the single light-pulse method and temperature dependence, we have proved that a structural mutation might be involved in high UV-sensitivity in Norin 1.3 Effect of UVB radiation on protein contents in leaves : We previously suggested that Rubisco rather than LHCII might be more influenced by supplemental UVB radiation during growth. Therefore, we studied the effects of UVB radiation (1) on the synthesis and degradation of Rubisco and LHCII using ィイD115ィエD1N as a tracer, and (2) on the mRNA transcript levels for Rubisco subunits (rbcS encoded in nuclear and rbcL encoded in chloroplast) and LHCII (cab encoded in nuclear, in leaves of UV-resistant and -sensitive rice. We found that the expression of nuclear encoded genes were more influenced than that of chloroplast by UVB, and that the expression of rbcL was more influenced than cab by UVB.