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 an abundant soluble protein in the C3 plant chloroplast; however, its function in photosynthetic carbon assimilation is not well defined. In this study we have examined the relationship between carbonic anhydrase (CA) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) expression during pea (Pisum sativum) development as well as in various tissues and cultivars. Although absolute levels of activity and transcript abundance for the two proteins can vary considerably during development, a relatively constant ratio of CA to Rubisco transcript abundance 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, also appear to maintain an invariant CA:Rubisco ratio. These data are discussed with respect to gene copy number, regulation of expression, and the proposed role of CA in photosynthetic carbon fixation.