Photoinhibition of chloroplast reactions. I. Kinetics and action spectra.

A study was made of photoinhibition of spinach chloroplast reactions. The kinetics and spectral characteristics of the photoinhibition over a range between 230 and 700 mmu have been examined. The decline of activity due to preillumination was independent of wavelength, and dependent upon the number of quanta applied, not upon the rate of application. The effectiveness spectra of photoinhibition indicate that active ultraviolet light is absorbed by a pigment which is not a normal light absorber for photosynthesis and acts with a high quantum efficiency (> 0.1) for photoinhibition.Active visible light is absorbed by the pigments which sensitize photosynthesis (chlorophyll, carotenoids). A very low quantum efficiency (about 10(-4)) was observed for the photoinhibition with visible light.The action spectrum of the photoinhibition of dye reduction by chloroplasts and lyophylized Anacystis cells indicated that the damage caused by visible light is due to quanta absorbed by photosystem II. However, since system I might not be involved in dye reduction, the spectra may reflect only damage to photosystem II.