UVB-INDUCED CYCLOBUTYL PYRIMIDINE DIMER AND PHOTOREPAIR WITH PROGRESSOF GROWTH AND LEAF AGE IN RICE

We have examined the susceptibility to cyclobutyl pyrimidine dimer (CP D) induction by UVB radiation, the ability to photorepair cyclobutyl p yrimidine dimers (CPDs), and the levels of ultraviolet (UV)-absorbing compounds in various developing stages of leaves in UVB-resistant (Sas anishiki) and -sensitive (Norin 1) rices (Oryza sativa L.).UVB produce s more CPDs in the second, third and fourth fully expanded leaves than in the fifth and sixth fully expanded leaves. In leaves in which the levels of UV-absorbing compounds are lower, more CPDs are produced. Th e ability to photorepair CPDs in fully expanded leaves of different st ages of each cultivar remains approximately constant, although the pho torepair capacity in the fourth leaf rapidly increases fi-om leaf emer gence until full expansion. The photorepair capacity is lower in Norin 1 than that in Sasanishiki in all the leaf stages or different aged l eaves. These results therefore suggest that rice plants could be more susceptible to CPD induction at the stage when the second, third or fo urth leaves are developing, and UVB sensitivity correlates with low CP D photorepair. (C) 1998 Elsevier Science S.A. All rights reserved.