Developmental and Varietal Comparisons of Pod Carboxylase Levels in Pisum sativum L.

The activities of phosphoenolpyruvate (PEP) carboxylase andribulose-1, 5-bisphosphate (RuDP) carboxylase have been determinedin the developing pod walls of six genotypes of Pisum sativum.Genotypes were chosen which varied in pod characters such aschlorophyll content and tissue morphology, which it was hopedwould be associated with variation in carboxylase levels. Whilst both enzymes were detected in all genotypes, the levelsof activity varied considerably with pod type and with age.In general RuDP carboxylase activity correlated with chlorophyllconcentration, and yellow podded types had considerably lessactivity than green types. The yellow podded genotypes, however,contained significantly higher levels of PEP carboxylase which,in terms of total carboxylase activity, compensated for thelower RuDP carboxylase levels. The activities of both enzymes were determined within the endocarpand within the mesocarp plus exocarp, using 16-day-old pods.All genotypes showed an enrichment for PEP carboxylase in theendocarp and all but one genotype showed a similar enrichmentfor RuDP carboxylase activity in this layer. The role of the carboxylase enzymes within the pod wall is discussedand it is suggested that their main function may be to maintainan appropriate level of CO₂ within the pod cavity as well asrecycling carbon to the developing seeds. Pisum savitum L., pea, pods, carboxylase levels, genetic variation