CORRELATION OF CARBONIC-ANHYDRASE AND RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE OXYGENASE EXPRESSION IN PEA/

The enzyme carbonic anhydrase (carbonate dehydratase, EC 4.2.1.1) is a n abundant soluble protein in the C-3 plant chloroplast; however, its function in photosynthetic carbon assimilation is not well defined. In this study we have examined the relationship between carbonic anhydra se (CA) and ribulose-l,5-bisphosphate carboxylase/oxygenase (Rubisco) expression during pea (Pisum sativum) development as well as in variou s tissues and cultivars. Although absolute levels of activity and tran script abundance for the two proteins can vary considerably during dev elopment, a relatively constant ratio of CA to Rubisco transcript abun dance and enzyme activity appears to be initiated during greening and maintained in mature and senescing photosynthetic tissue. Various pea cultivars, although exhibiting differing amounts of Rubisco and CA, al so appear to maintain an invariant CA:Rubisco ratio. These data are di scussed with respect to gene copy number, regulation of expression, an d the proposed role of CA in photosynthetic carbon fixation.