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pubmed:abstractText |
Photoinhibition of photosystem II (PSII) electron transport and subsequent degradation of the D1 protein were studied in pumpkin (Cucurbita pepo L.) leaves developed under high (1000 mumol m(-2) s(-1)) and low (80 mumol m(-2) s(-1)) photon flux densities. The low-light leaves were more susceptible to high light. This difference was greatly diminished when illumination was performed in the presence of chloramphenicol, indicating that a poor capacity to repair photodamaged PSII centers is decisive in the susceptibility of low-light leaves to photoinhibition. In fact, the first phases of the repair cycle, degradation and removal of photodamaged D1 protein from the reaction center complex, occurred slowly in low-light leaves, whereas in high-light leaves the degradation of the D1 protein more readily followed photoinhibition of PSII electron transport. A modified form of the D1 protein, with slightly slower electrophoretic mobility than the original D1, accumulated in the appressed thylakoid membranes of low-light leaves during illumination and was subsequently degraded only slowly.
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