DEVELOPMENTAL AND CIRCADIAN PATTERN OF RUBISCO ACTIVASE MESSENGER-RNAACCUMULATION IN APPLE PLANTS

An apple cDNA encoding the precursor of ribulose 1,5-bisphosphate carb oxylase/oxygenase (rubisco) activase has been characterized. Using thi s cDNA as a probe, leaf-specific and light-regulated accumulation of c orresponding transcripts was detected. Rubisco activase transcripts al so turned out to accumulate at growing levels during apple leaf develo pment, to reach a maximum in fully expanded leaves. In contrast, chlor ophyll a/b-binding protein (Cab) and rubisco large subunit mRNA levels reach a maximum earlier in the course of leaf development. Moreover, the accumulation of rubisco activase messengers appeared to follow an oscillating circadian rhythm qualitatively similar to that observed fo r Cab mRNA levels.