Action spectra of the three light reactions in photosynthesis

Abstract

Action spectra for the photoreduction of cytochrome b 559 and C550 and for the photooxidation of cytochromes b 559 and f in spinach chloroplasts were measured in the region from 640 to 720 nm. The action spectra for the photoreduction of cytochrome b 559 and C550 are closely similar and show marked decreases in efficiency at wavelengths longer than 680 nm. These findings are consistent with the conclusion that the two components are reduced by the same photoact of Photosystem II. The action spectrum for the photooxidation of cytochrome b 559 also showed a decrease in efficiency at wavelengths longer than 680 nm, characteristic of Photosystem II, but the photooxidation of cytochrome f showed an increase in efficiency at long wavelengths, characteristic of Photosystem I. These action spectra show a pattern consistent with a recently proposed concept of three light reactions in plant photosynthesis.