EFFECTS OF LIGHT ENVIRONMENT DURING CULTURE ON UV-INDUCED 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 t o photorepair CPD, The steady-state CPD level in plants grown under vi sible radiation with supplemental UVB radiation in a growth chamber wa s several times higher than in plants grown without supplemental UVB r adiation, whereas in outdoor-grown plants, it was not enhanced by supp lemental UVB radiation. The susceptibility to CPD induction by challen ge UVB exposure was highest in dark-grown plants and decreased with in creasing irradiance of visible radiation at low and high levels and ou tdoors. Chronic UVB radiation reduced the susceptibility to UV-induced CPD in plants grown both indoors and outdoors. There was a significan t negative correlation between CPD levels induced by challenge UVB exp osure and the content of UV-absorbing compounds. The UV-induced CPD co uld be reduced by subsequent blue radiation in all samples except in d ark-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.