High Salt Stress in Coupled and Uncoupled Thylakoid Membranes: A Comparative Study

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P. Mehta¹, A. Jajoo^1*, S. Mathur¹, S. I. Allakhverdiev², and S. Bharti¹

¹School of Life Sciences, Devi Ahilya University, Indore 452017, M.P., India; E-mail: anjanajajoo@hotmail.com

²Institute of Basic Biological Problems, Pushchino, Moscow Region, Russia

^* To whom correspondence should be addressed.

Received October 13, 2008; Revision received December 11, 2008

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The effect of high salt concentration on photosystem II (PS II) electron transport rates and chlorophyll a fluorescence induction kinetics was investigated in coupled and uncoupled spinach thylakoid membranes. With increase in salt concentration, the rates of electron transport mediated by PS II and the F_v/F_m ratio were affected more in uncoupled thylakoids as compared to coupled thylakoid membranes. The uncoupled thylakoid membranes seemed to behave like coupled thylakoid membranes at high NaCl concentration (~1 M). On increasing the salt concentration, the uncoupler was found to be less effective and Na⁺ probably worked as a coupling enhancer or uncoupling suppressor. We suggest that positive charge of Na⁺ mimics the function of positive charge of H⁺ in the thylakoid lumen in causing coupled state. The function of NaCl (monovalent cation) could be carried out by even lower concentration of Ca²⁺ (divalent cation) or Al³⁺ (trivalent cation). We conclude that this function of NaCl as coupling enhancer is not specific, and in general a positive charge is required for causing coupling in uncoupled thylakoid membranes.

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KEY WORDS: high salt stress, uncoupler, PS II and PS I, electron transport, thylakoid membranes

DOI: 10.1134/S0006297909060054

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