Reversible membrane reorganizations during photosynthesis in vivo: revealed by small-angle neutron scattering

Abstract

In the present study, we determined characteristic repeat distances of the photosynthetic membranes in living cyanobacterial and eukaryotic algal cells, and in intact thylakoid membranes isolated from higher plants with time-resolved small-angle neutron scattering. This non-invasive technique reveals light-induced reversible reorganizations in the seconds-to-minutes time scale, which appear to be associated with functional changes in vivo.

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

“…In general, these results, in line with similar observations [29,39,[41][42][43], underline the remarkable flexibility of the thylakoid membrane ultrastructure, which should thus not be portrayed as simply providing a scaffold for the photosynthetic functions but also actively participating in the energy conversion steps and in different regulatory functions.…”

“…It is important to note that the low-pH induced variations in the SANS profiles and the underlying structural reorganizations of the thylakoid membranes reported here are very similar to those observed earlier upon illumination of isolated thylakoid membranes [29,39]. Since illumination induces the acidification of the lumen in the thylakoid membranes, the present results further support our earlier conclusion that variations in the periodic arrangement of plant thylakoid membranes -evidently in concert with other membrane reorganizations (see Introduction) -participate in NPQ, a key photoprotective mechanism of green plants.…”

“…This acidification-induced reversible shrinkage of the thylakoid membranes strongly resembles the effect of illumination, observed earlier on isolated thylakoid membranes [29,32,39,40].…”

“…As reported earlier [39], the SANS signal of magnetically oriented thylakoid membranes is dominated by well discernible scattering peaks with maxima on the 2D image in the direction parallel with the direction of the applied magnetic field ( Figure 1A). Upon acidification of the suspension medium the observed diffraction peak became more flat and the Bragg peaks largely diminished ( Figure 1B).…”

“…Resuspending the low-pH treated thylakoid membranes in p 2 H 8.0 medium largely restored the original 2D profile ( Figure 1C) with well-defined Bragg peaks. It is interesting to note that these low-pH induced variations in the 2D SANS profiles closely resemble the ∆pH-dependent light-induced changes in the 2D scattering profiles of isolated thylakoid membranes [29,32,39]. In order to obtain quantitative information about the low-pH induced reorganization of the thylakoid membranes we performed sectorial averaging of the 2D scattering curves -allowing determination of the diffraction peak (and hence the RD of the thylakoid membranes), and also investigated the angular dependency of the 2D scattering signal around the diffraction peak.…”