title: Slow degradation of the d1 protein is related to the susceptibility of low-light-grown pumpkin plants to photoinhibition.
abstract: 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.
authors.affiliation: Department of Biology, University of Turku, SF 20700 Turku, Finland.
authors.forename: E
authors.initials: E
authors.lastname: Tyystjärvi
authors.forename: K
authors.initials: K
authors.lastname: Ali-Yrkkö
authors.forename: R
authors.initials: R
authors.lastname: Kettunen
authors.forename: E M
authors.initials: EM
authors.lastname: Aro