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MAGNESIUM ION EFFECTS ON CHLOROPLAST PHOTOSYSTEM II FLUORESCENCE AND PHOTOCHEMISTRY
Author(s) -
Henkin Bruce M.,
Sauer Kenneth
Publication year - 1977
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.1751-1097.1977.tb07485.x
Subject(s) - photosystem ii , photochemistry , fluorescence , chemistry , divalent , chloroplast , tricine , photosynthesis , hill reaction , dithionite , dcmu , oxygen evolution , electrochemistry , biochemistry , physics , organic chemistry , quantum mechanics , electrode , gene , enzyme
Abstract. –Although there have been several reports that divalent cations, especially Mg 2+ , can significantly affect chloroplast photoprocesses, the molecular mechanism of cation interaction is not well understood. We have investigated the interaction of Mg 2+ with Photosystem II photoprocesses by studying cation effects on chloroplast fluorescence and the Hill reaction. Our results are summarized as follows. 1. Mg 2+ stimulation of background fluorescence (20–30%) saturates at about 0.5 mM Mg 2+ , while Mg 2+ stimulation of variable fluorescence (250%) saturates at about 2.5 mM Mg 2+ . 2. Addition of Mg 2+ to chloroplasts treated with 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea or dithionite causes a doubling in the amount of total (background + variable) fluorescence. 3. Studies on chloroplasts in the presence of 2,6‐dichlorophenolindophenol indicate that Mg 2 doubles the relative yield of variable fluorescence under light‐limiting conditions. 4. Mg 2 causes large (70–120%) increases in the light‐limited rate of the DCIP Hill reaction. We interpret these results in terms of a model involving two components of chloroplast emission. Our analysis indicates that Mg 2+ increases the effective absorption cross section (size) of the pigment array associated with Photosystem II photochemistry.