Seasonal changes in photosynthesis, protein composition and mineral content in Rhododendron leaves

Seasonal changes in the proteome, specific leaf weight, mineral content, pigment content and photosynthetic properties were determined in leaves of a cultivar of Rhododendron catawbiense harvested in the field (2001–2004). Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) revealed that several dehydrin-like proteins, strongly expressed in the winter acclimated samples, disappeared during the transition to spring. Photosynthetic carbon assimilation, electron transport and the quantum yield for photosystem II (Fv/Fm) were severely down-regulated in winter acclimated leaves. Xanthophyll cycle pigments increased 2.3-fold in winter acclimated leaves. When winter acclimated leaves were brought into more favorable temperature conditions, the capacity of carbon assimilation fully recovered over a period of approximately 14 days. The recovery was linear and rapid for the first 4 days yielding 60% of the fully recovered rate. Electron transport rates (ETR) recovered more rapidly (80% recovery in 24 h) than carbon assimilation. The linear phase of the ETR recovery was slightly inhibited by protein synthesis inhibitors streptomycin and chloramphenicol, but more markedly by cycloheximide (44% inhibition). The slow recovery phase was impacted by all of the protein synthesis inhibitors with cycloheximide having the most profound effect (58% inhibition at 48 h). Specific leaf weight increased by 48% in winter acclimated leaf samples relative to late summer. Leaf calcium and magnesium contents were reduced (24% and 17%, respectively) in winter relative to late summer samples. An opposite pattern was seen for sulfur and phosphate (winter increases of 28% for sulfur and 72% for phosphate).