EFFECT OF BLUE-LIGHT AND RED-LIGHT ON THE CONTROL OF CHLOROPLAST ACCLIMATION OF LIGHT-GROWN PEA LEAVES TO INCREASED FLUENCE RATES

We have investigated the possibility of the involvement of a blue ligh t fluence-rate sensing photoreceptor in the light acclimation of chlor oplast components in light-grown pea seedlings. Low light-grown seedli ngs were acclimated for 2 days to either 20 or 200 mu mol m(-2) s(-1) of white, blue-enriched, or broad-band red light. An increase in blue- enriched light fluence rate was more effective than that of red light in bringing about both inhibition of internode growth and the enhancem ent of the chlorophyll a/b ratio. Ribulose 1,5-bisphosphate carboxylas e/oxygenase and cytochrome f protein levels, per unit cell, also incre ased more markedly (around two-fold) in response to an increase in blu e light. The 23 kDa polypeptide of the oxygen-evolving complex and the light-harvesting chlorophyll alb protein of photosystem II apoprotein levels varied under all wavelengths to a lesser extent, correlating w ith total protein levels or greening. These data are consistent with t he hypothesis of a role for a blue photoreceptor in detecting low vers us high fluence rate of light, and subsequently controlling the light acclimation responses. Nevertheless photosynthesis or other mechanisms of fluence-rate photoperception must also be involved.