Abstract
During autumn senescence, plants must disassemble the photosynthetic apparatus as nutrients are remobilized from the leaves. The goal of this study was to examine changes in relative abundance of photosynthetic proteins and pigments throughout autumn senescence in order to understand the mechanisms of photoprotection used during this process. We sampled leaves from two deciduous tree species [sugar maple (Acer saccharum Marsh.) and swamp white oak (Quercus bicolor Willd.)] throughout autumn during 2010 and 2013. Chlorophyll fluorescence was measured, thylakoids were isolated for western blotting with antibodies to individual proteins and pigment content was assessed. Both species retained high photochemical efficiency until late autumn and showed earlier onset of degradation of photosystem I relative to photosystem II. The species differed in the timing and pattern of degradation of individual photosynthetic proteins and pigments. In maple, there were increases in anthocyanins, more rapid degradation of light-harvesting proteins and enrichment of xanthophyll cycle pigments in late autumn. In oak, light-harvesting proteins were retained in higher abundance throughout autumn, PsbS levels increased during early autumn and lutein was enriched in late autumn samples. The results suggest that the species differ in strategies for photoprotection during autumn senescence.