Investigation of the Lateral Light-induced Migration of Photosystem II Light-harvesting Proteins by Nano-high Performance Liquid Chromatography Electrospray Ionization Mass Spectrometry

Abstract

This study reports a detailed analysis of the light-induced lateral migration of the photosystem II (PSII) antennae between appressed and non-appressed thylakoid membranes. The relative PSII antennae that migrated to stroma lamellae were readily established on the basis of peak areas of the separated stroma proteins in the ultraviolet chromatograms. Phosphorylation was predicted by intact molecular mass measurements, and this was confirmed by immunoblotting. When thylakoid membrane and chloroplasts were illuminated at 100 microE m(-2)s(-1), light-harvesting complex type II (Lhcb2) was the first PSII antenna to migrate, preferentially in phosphorylated form. However, the amount of Lhcb2 that migrated decreased after the first 20 min when the total amount of the three different Lhcb1 isoforms (1.1, 1.2, and 1.3) reached maximum. Lhcb1.1 was always found in the unphosphorylated form and migrated later than the other two isoforms, although the latter were also found to have low levels of phosphorylation. At the same time, major antennae on the grana were not found to be phosphorylated, whereas Lhcb4 showed a significant increase in molecular mass. At higher light intensity Lhcb2 migration was negligible, whereas migration of Lhcb1 isoforms was little changed, increasing in irradiated chloroplasts. Because there was no significant phosphorylation at high light intensity, and yet pigments were found to have significantly increased on the stroma lamellae, it may be that pigments play a role in migration and that, in fact, there is no direct correlation between phosphorylation and migration. We hypothesize that the Lhcb1 isoforms expressed by the multigene families play a role in plant adaptation.