An attemlpt was made to localize the site of photoinhibition of photosynthesis by measuring the decay of various chloroplast reactions after exposure to very strong light. A11 substrate reductions coupled to oxygen evolution as well as photophosphorylation mediated by PMS, proved equally sensitive to photoinhibition. Reactions involving only the long wave photosystem, such as TPN reduction with ascorbate as electron donor and photooxidation of cytochromec by detergent‐treated chloroplasts were sensitive to a lower degree. Photoinhibition irreversibly annihilated the ‘variable’ fraction of fluorescence emission —it decreased the steady state yield 2‐3 fold and abolished the slow rise of the emission at the onset of illurnination. It is concluded that the primary site of light inactivation is in, or close to, the trapping centers of the oxygen evolving step of photosynthesis. Pre‐illumination leaves these traps in a state capable of draining light from sensitizing pigments but unable to perform useful photochemistry.
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Kok et al. (1965) studied this question.
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