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Amplified Degradation of Photosystem II D1 and D2 Proteins under a Mixture of Photosynthetically Active Radiation and UVB Radiation: Dependence on Redox Status of Photosystem II
Author(s) -
Babu Tripuranthakam S.,
Jansen Marcel A. K.,
Greenberg Bruce M.,
Gaba Victor,
Malkin Shmuel,
Mattoo Autar K.,
Edelman Marvin
Publication year - 1999
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1999.tb03326.x
Subject(s) - photosystem ii , degradation (telecommunications) , photochemistry , chemistry , redox , oxidizing agent , photosynthesis , photosynthetically active radiation , photosynthetic reaction centre , photoprotection , biophysics , biochemistry , electron transfer , biology , inorganic chemistry , organic chemistry , telecommunications , computer science
Abstract— Plants exposed to a mixture of photosynthetically active radiation (PAR) and UVB radiation exhibit a marked boost in degradation of the D1 and D2 photosysteni II (PS II) reaction center proteins beyond that predicted by the sum of rates in PAR and UVB alone (amplified degradation). Becausee degradation driven by visible or UVB radiation alone is uncoupled from PS II redox status, it was therefore assumed that the mixed‐light‐amplified component of degradation would behave similarly. Surprisingly, amplified degradation proved to be coupled tightly to the redox status of PS II. We show that inactivation of the PS II water oxidation by heat shock or oxidation of the plastosemiquinone (Q A ‐) by silicomolybdate nullifies only the amplified component of degradation but not the basic rates of degradation under PAR or UVB alone. The data are interpreted to indicate that formation of plastosemiquinone or an active water‐oxidizing Mn 4 cluster, is the UVB chromophore involved in amplified degradation of the D1 and D2 proteins. Furthermore, accumulation of Q A ‐by 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea or 2‐bromo‐3‐methyl‐6‐isopropyl‐4‐nitrophenol stimulated the mixed‐light‐amplified degradation component. Thus, amplified degradation of the D1 and D2 proteins in mixed radiance of PAR plus UVB (which simulates naturally occurring radiance) proceeds by a mechanism clearly distinct from that involved in degradation under PAR or UVB alone.