Correlation between thylakoid stacking and cation-induced decrease in photosystem I electron transport at saturating light intensity |
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Authors: | P Ramanujam Salil Bose |
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Institution: | School of Biological Sciences, Madurai Kamaraj University, Madurai 625 021, India |
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Abstract: | A Mg2+-induced decrease of the rate of photosystem I (PS I) electron transport (DCIPH2 → methyl viologen) in thylakoids under saturated light intensities has been reported earlier (S. Bose, J. E. Mullet, G. E. Hoch, and C. J. Arntzen, 1981, Photobiochem. Photobiophys.2, 45–52). A similar effect is observed with Na+, although the concentration required for half-maximal inhibition was higher by about two orders of magnitude. The cation effect was gradually abolished as the thylakoids were aged by incubation at 30 °C for 6 h. The loss of cation effect on PS I electron transport rate during aging was parallel to the corresponding loss of cation effect on thylakoid stacking. The cation concentration required for thylakoid stacking and the degree of inhibition as a function of cation concentration correlated strongly with the degree of thylakoid stacking. These observations indicated that the inhibition of the rate of PS I electron transport by cations is a consequence of cation-induced stacking of thylakoid membranes. The observed inhibition of the rate of PS I electron transport is discussed in terms of two hypotheses: (i) a fraction (20–30%) of the PS I complexes is trapped in the appressed region of grana and becomes unavailable to the electron donor (DCIPH2) and (ii) the membrane structure is altered by the cations in such a manner that the rate constant of electron donation by the donor to the electron transport chain in the thylakoid is decreased. |
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Keywords: | Author to whom reprint requests should be addressed |
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