Low-pH induced reversible reorganizations of chloroplast thylakoid membranes - as revealed by small-angle neutron scattering

Abstract

AbstractEnergization of thylakoid membranes brings about the acidification of the lumenal aqueous phase, which activates important regulatory mechanisms. Earlier Jajoo and coworkers (2014 FEBS Lett. 588:970) have shown that low pH in isolated plant thylakoid membranes induces changes in the excitation energy distribution between the two photosystems. In order to elucidate the structural background of these changes, we used small-angle neutron scattering on thylakoid membranes exposed to low p2H and show that gradually lowering the p2H from 8.0 to 5.0 causes small but well discernible reversible diminishment of the periodic order and the lamellar repeat distance and an increased mosaicity – similar to the effects elicited by light-induced acidification of the lumen. Our data strongly suggest that thylakoids dynamically respond to the membrane energization and actively participate in different regulatory mechanisms.HighlightsThylakoid membranes exposed to low p2H studied by small-angle neutron scatteringAcidification causes reversible shrinkage and diminished lamellar orderSANS changes induced by low pH resemble those due to light-induced lumenal acidificationAbbreviationsNPQnon-photochemical quenchingqEthe energy-dependent component of NPQΔμH+transmembrane electrochemical potential gradientPSIphotosystem IPSIIphotosystem IILETlinear electron transportCDcircular dichroismSANSsmall-angle neutron scatteringqscattering vector or momentumtransferIintensityq*center position of the Bragg peakRDrepeat distanceφazimuthal angleI(φ)angular dependency of the scattering intensityFWHMfull width at half maximum