Seasonal variations of leaf chlorophyll–protein complexes in the wintergreen herbaceous plant Ajuga reptans L.

Abstract

The chlorophyll and carotenoid content, and the spectra of low-temperature fluorescence of the leaves, chloroplasts and isolated pigment–protein complexes in the perennial herbaceous wintergreen plant Ajuga reptans L. (bugle) in different seasons of the year were studied. During winter, these plants downregulate photosynthesis and the PSA is reorganised, including the loss of chlorophyll, possible reductions in the number of functional reaction centres of PSII, and changes in aggregation of the thylakoid protein complexes. We also observed a restructuring of the PSI–PSII megacomplex and the PSII–light-harvesting complex II supercomplex in leaves covered by snow. After snowmelt, the monomeric form of the chl a/b pigment–protein complex associated with PSII (LHCII) and the free pigments were also detected. We expect that snow cover provides favourable conditions for keeping photosynthetic machinery ready for photosynthesis in spring just after snowmelt. During winter, the role of the zeaxanthin-dependent protective mechanism, which is responsible for the dissipation of excess absorbed light energy, is likely to increase.