RECOVERY FROM PHOTOINHIBITION IN PEAS (PISUM-SATIVUM L) ACCLIMATED TOVARYING GROWTH IRRADIANCES - ROLE OF D1 PROTEIN-TURNOVER

D1 protein turnover and restoration of the photochemical efficiency of photosystem II (PSII) after photoinhibition of pea leaves (Pisum sati vum L. cv Greenfeast) acclimated to different light intensities were i nvestigated. All peas acclimated to different light intensities were a ble to recover from photoinhibition,, at least partially, at light int ensities far above their growth light irradiance. However, the capacit y of pea leaves to recover from photoinhibition under increasing-high irradiances was strictly dependent on the light acclimation of the lea ves; i.e. the higher the irradiance during growth, the better the capa city of pea leaves to recover from photoinhibition at moderate and hig h light. In our experimental conditions, mainly D1 protein turnover-de pendent recovery was monitored, since in the presence of an inhibitor of chloroplast-encoded protein synthesis, lincomycin, only negligible recovery took place. In darkness, neither the restoration of PSII phot ochemical efficiency nor any notable degradation of damaged D1 protein took place. In low light, however, good recovery of PSII occurred in all peas acclimated to different light intensities and was accompanied by fast degradation of the D1 protein. The rate of degradation of the D1 protein was estimated to be 3 to 4 times faster in photoinhibited leaves than in nonphotoinhibited leaves under the recovery conditions of 50 mu mol of photons m(-2) s(-1). In moderate light of 400 mu mol o f photons m(-2) s(-1), the photoinhibited low-light peas were not able to increase further the rate of D1 protein degradation above that obs erved in nonphotoinhibited leaves, nor was the restoration of PSII fun ction possible. On the other hand, photoinhibited high-light leaves we re able to increase the rate of D1 protein degradation above that of n onphotoinhibited leaves even in moderate and high light, ensuring at l east partial restoration of PSII function. We conclude that the capaci ty of photoinhibited leaves to restore PSII function at different irra diances was directly related to the capacity of the leaves to degrade damaged D1 protein under the recovery conditions.