Effects of Light Environment During Culture on UV-lnduced Cyclobutyl Pyrimidine Dimers and Their Photorepair in Rice (Oryza sativa L.)

— We examined the effects of a light environment during culture of rice plants (Oryza sativa) on the steady-state cyclobutyl pyrimidine dimer (CPD) level, CPD induction by challenge UVB exposure and the ability to photorepair CPD. The steady-state CPD level in plants grown under visible radiation with supplemental UVB radiation in a growth chamber was several times higher than in plants grown without supplemental UVB radiation, whereas in outdoor-grown plants, it was not enhanced by supplemental UVB radiation. The susceptibility to CPD induction by challenge UVB exposure was highest in dark-grown plants and decreased with increasing irradiance of visible radiation at low and high levels and outdoors. Chronic UVB radiation reduced the susceptibility to UV-induced CPD in plants grown both indoors and outdoors. There was a significant negative correlation between CPD levels induced by challenge UVB exposure and the content of UV-absorbing compounds. The UV-induced CPD could be reduced by subsequent blue radiation in all samples except in dark-grown seedlings. The higher the irradiance of visible radiation in the culture, the greater the ability to photorepair CPD. Chronic UVB radiation did not increase the ability to photorepair CPD.