Expression of photosynthesis- and senescence-related genes during leaf development and senescence in silver birch (Betula pendula) seedlings

Leaf development and senescence were studied in greenhouse-grown silver bir ch (Betula pendula Roth) seedlings over a period of 7 weeks. Prior to the e xperiment, leaves from 100 seedlings were marked for five sampling dates. T iming of the developmental phases was studied with biochemical analyses of total soluble protein, Rubisco protein, chlorophyll concentration and at th e level of gene expression related to photosynthesis, energy metabolism, et hylene synthesis and protein degradation. During the sampling period, an in itial increase in photosynthetic capacity could be seen, when expression of the Rubisco small subunit gene (RbcS) and Rubisco protein (EC 4.1.1.39) we re examined. Down-regulation of photosynthesis, visible as a decrease in Ru bisco protein and RbcS mRNA, started soon after full expansion of the leave s and processes related to senescence followed. mRNA accumulation for the e thylene-forming enzyme 1-aminocyclopropane-1-carboxylic acid oxidase increa sed first during the onset of senescence. Protein degradation was observed as a loss of soluble proteins, with a simultaneous increase in the leucine aminopeptidase (EC 3.4.11.1) mRNA levels. The mRNA levels of ribonuclease-l ike pathogenesis-related protein 10 also increased clearly during senescenc e, but the mitochondrial phosphate translocator mRNA showed only a slight i ncrease. Chlorophyll concentration of the leaves decreased after the mRNA l evels of these senescence-related gents had become more abundant.