Biosynthesis and degradation of Rubisco during ovary senescence and fruit development induced by gibberellic acid in Pisum sativum

The concentration, biosynthesis and proteolytic degradation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) and the level of the transcripts of the large and the small subunits were studied in unpollinated ovaries of Pisum sativum L. cv. Alaska during the early stages of ovary senescence and during early parthenocarpic fruit development induced by gibberellic acid (GA). De novo synthesis of Rubisco during fruit development is associated with both an activation of protein synthesis and an increase of the mRNA levels, especially of those for the small subunit of the protein. However, in senescent ovaries, senescence-specific proteolysis seems to be the operating mechanism controlling Rubisco level as supported by the following observations: (1) Rubisco cleavage fragments of 52 and 30 kDa were detected in crude extracts from senescent ovaries, but these in-vivo-produced polypeptides were not present in extracts from either presenescent or GA-treated ovaries; (2) a new proteolytic activity at neutral pH and an enhancement of acidic proteolytic activity were detected in an in vitro assay only in extracts of senescent ovaries.