Cost and benefit of the repair of photodamaged photosystem II in spinach leaves: roles of acclimation to growth light
When visible light is excess, the photosynthetic machinery is photoinhibited. The extent of net photoinhibition of photosystem II (PSII) is determined by a balance between the rate of photodamage to D1 and some other PSII proteins and the rate of the turnover cycle of these proteins. It is widely believed that the protein turnover requires much energy cost. The aims of this study are to (1) evaluate the energy cost of PSII repair, (2) measure the benefit in terms of photosynthetic gain realized by the repairing of the photodamaged PSII, and (3) know whether acclimation of photosynthesis to growth light affects the rates of the photodamage and repair. We grew spinach in high-light (HL) and low-light (LL) and measured the rates of D1 photodamage and repair in these leaves. We determined the rate constants of photodamage (k pi) and repair (k rec) by the PAM fluorometry in the presence or in the absence of lincomycin, an inhibitor of 70S protein synthesis. HL leaves showed smaller k pi and greater k rec than LL leaves. The energy cost of the repairing of the photodamaged D1 protein was <0.5 % of ATP produced by photophosphorylation at PPFDs ranging from 400 to 1600 μmol m−2 s−1 and was greater in HL leaves than in LL leaves. The benefits brought about by the repair were more than from 35 to 270 times the cost at PPFDs ranging from 400 to 1600 μmol m−2 s−1. The benefits of HL leaves were greater than those of LL leaves because of the higher photosynthesis rates in HL leaves. Running a simple simulation of daily photosynthesis using the parameters obtained in this study, we discuss why the plants need to pay the cost of D1 protein turnover to repair the photodamaged PSII.
KeywordsChlorophyll fluorescence D1 protein turnover Excess energy Light acclimation Photoinhibition Photosystem II
We thank Dr. Riichi Oguchi and Mr. Masaru Kono for kind support and advice. We also thank Prof. Chikahiro Miyake (Kobe University) for a useful discussion concerning the ATP production rate. We are grateful to two anonymous reviewers and the handling editor, Dr. Shizue Matsubara, for their very constructive comments. The last author (IT.) once studies as a postdoctoral fellow under the supervision of Prof. Barry Osmond, and deeply thanks for his continuous encouragement.
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