Abstract
BackgroundNon photochemical reduction of PQ pool and mobilization of LHCII between PSII and PSI are found to be linked under abiotic stress conditions. The interaction of non photochemical reduction of PQ pool and state transitions associated physiological changes are critically important under anaerobic condition in higher plants.Methodology/FindingsThe present study focused on the effect of anaerobiosis on non-photochemical reduction of PQ pool which trigger state II transition in Arabidopsis thaliana. Upon exposure to dark-anaerobic condition the shape of the OJIP transient rise is completely altered where as in aerobic treated leaves the rise is unaltered. Rise in F o and F J was due to the loss of oxidized PQ pool as the PQ pool becomes more reduced. The increase in Fo′ was due to the non photochemical reduction of PQ pool which activated STN7 kinase and induced LHCII phosphorylation under anaerobic condition. Further, it was observed that the phosphorylated LHCII is migrated and associated with PSI supercomplex increasing its absorption cross-section. Furthermore, evidences from crr2-2 (NDH mutant) and pgr5 mutants (deficient in non NDH pathway of cyclic electron transport) have indicated that NDH is responsible for non photochemical reduction of the PQ pool. We propose that dark anaerobic condition accelerates production of reducing equivalents (such as NADPH by various metabolic pathways) which reduce PQ pool and is mediated by NDH leading to state II transition.Conclusions/SignificanceAnaerobic condition triggers non photochemical reduction of PQ pool mediated by NDH complex. The reduced PQ pool activates STN7 kinase leading to state II transition in A. thaliana.
Highlights
The light dependent reactions of photosynthesis involve electron transport through photosystems (PS), PSI and PSII in thylakoid membranes
This non photochemical reduction could be due to chlororespiration i.e. respiration-like electron transport from NAD(P)H to PQ pool in the thylakoid membranes mediated by NADPH dehydrogenase (NDH) and plastidial terminal oxidase (PTOX) [17,18,19]
Results with OJIP transients have shown that the drastic increase in J phase under anaerobic condition was due to reduced state of PQ pool
Summary
The light dependent reactions of photosynthesis involve electron transport through photosystems (PS), PSI and PSII in thylakoid membranes. A fraction of LHCII migrates to PSI by lateral diffusion; the opposite process occurs after dephosphorylation by phosphatase (PPH1/TAP38) [12,13,14] Such mechanism of state transitions occur under conditions irrespective of light due to dark reduction of PQ pool (non photochemical reduction) [15,16]. This non photochemical reduction could be due to chlororespiration i.e. respiration-like electron transport from NAD(P)H to PQ pool in the thylakoid membranes mediated by NADPH dehydrogenase (NDH) and plastidial terminal oxidase (PTOX) [17,18,19]. The interaction of non photochemical reduction of PQ pool and state transitions associated physiological changes are critically important under anaerobic condition in higher plants
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