Mechanism of action of anions on the electron transport chain in thylakoid membranes of higher plants

Abstract

With an aim to improve our understanding of the mechanisms behind specific anion effects in biological membranes, we have studied the effects of sodium salts of anions of varying valency in thylakoid membranes. Rates of electron transport of PS II and PS I, 77K fluorescence emission and excitation spectra, cyclic electron flow around PS I and circular dichroism (CD) spectra were measured in thylakoid membranes in order to elucidate a general mechanism of action of inorganic anions on photosynthetic electron transport chain. Re-distribution of absorbed excitation energy has been observed as a signature effect of inorganic anions. In the presence of anions, such as nitrite, sulphate and phosphate, distribution of absorbed excitation energy was found to be more in favor of Photosystem I (PS I). The amount of energy distributed towards PS I depended on the valency of the anion. In this paper, we propose for the first time that energy re-distribution and its valence dependence may not be the effect of anions per se. The entry of negative charge (anion) is accompanied by influx of positive charge (protons) to maintain a balance of charge across the thylakoid membranes. As reflected by the CD spectra, the observed energy re-distribution could be a result of structural rearrangements of the protein complexes of PS II caused by changes in the ionic environment of the thylakoid lumen.

The Arabidopsis thylakoid transporter PHT4;1 influences phosphate availability for ATP synthesis and plant growth

“…Psi‐type CD in vivo sensitively indicates minor changes in the protein composition of PSII–LHCII macro‐assemblies, the physiological states of plants (Garab et al ., ; Barzda et al ., ; Kovacs et al ., ; Dietzel et al ., ) and the ionic environment of membranes (Garab et al ., ). Psi‐type CD diminishes substantially upon the addition of Pi to isolated thylakoid membranes (Singh‐Rawal et al ., ). The diminished amplitude of the psi‐type CD in pht4;1 (Figure ) is in line with the above‐reported data, and strengthens the importance of the ionic environment, including Pi, for the long‐range order of LHCII–PSII supercomplexes.…”

Transport Across Chloroplast Membranes: Optimizing Photosynthesis for Adverse Environmental Conditions

“…By contrast, salt toxicity and inhibition of the photosynthesis in soybean were more dependent on the Cl À but not Na + accumulation in chloroplasts (Chen and Yu, 2007). A shift in anion balance shifted the solar energy distribution from PSII to PSI, affecting the function of the water-splitting complex and electron transport to and from the plastocyanin (Jajoo et al, 2001;Singh-Rawal et al, 2011). This is also true for cations, which affected light photosynthesis via modification of the membrane surface charge (Barber et al, 1977).…”

Towards a critical understanding of the photosystem II repair mechanism and its regulation during stress conditions

“…While talking of PSII repair cycle and distribution of various proteases as well as their interaction with damaged D1 protein, it becomes essential to describe the role of grana stacking and thylakoid membrane heterogeneity. Stacking and unstacking of thylakoid membranes are controlled by electrostatic interactions of the membrane surface in general [44] and thus is affected by the ionic environment around it [45,46]. Most likely, it is the hydrogen bonding and the electrostatic interactions that participate in membrane stacking.…”