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Light‐dependent inhibition of photosynthetic electron transport by zinc
Author(s) -
Baker Neil R.,
Fernyhough Paul,
Meek Ian T.
Publication year - 1982
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1982.tb00328.x
Subject(s) - chemistry , zinc , photosystem i , electron transport chain , thylakoid , photosystem , light intensity , photochemistry , photosystem ii , photosynthesis , p700 , biophysics , chloroplast , biochemistry , biology , organic chemistry , physics , optics , gene
The effects of zinc concentrations up to 400 μ M were examined on three photosynthetic electron transport reactions of thylakoids isolated from Pisum sativum L. cv. Meteor. Zinc (400 μ M ) had no effect on photosystem I mediated electron transport from reduced N,N,N′,N′‐tetramethyl‐ p ‐phenylenediamine to methyl viologen, but inhibited uncoupled electron flow from water to methyl viologen by ca 50% and to 2,6‐dichlorophenol‐indophenol (DCPIP) by ca 30% at saturating light levels. Zinc inhibition of DCPIP photoreduction was independent of the light intensity to which thylakoids were exposed. Decreasing the photon flux density below 400 μmol m −2 s −1 produced a logarithmic reduction in the zinc‐induced inhibition of methyl viologen photoceduction; a stimulation of this reaction was observed below 80 μmol photons m −2 s −1 . Increasing light intensity decreased the amount of zinc tightly bound to the thylakoid membranes, but increased the weakly associated zinc which could be removed by washing the membranes with buffer containing Mg 2 . The results suggest that zinc acts on the photosynthetic electron transport system at two sites. Site 1 is on the oxidizing side of photosystem 2 and the inhibition by zinc is independent of the light intensity. Site 2 is between photosystems 1 and 2 and the electron flow can be positively or negatively affected by zinc depending on the light intensity.