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

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Abstract
The activities of phosphoenolpyruvate (PEP) carboxylase and ribulose-1, 5-bisphosphate (RuDP) carboxylase have been determined in the developing pod walls of six genotypes of Pisum sativum. Genotypes were chosen which varied in pod characters such as chlorophyll content and tissue morphology, which it was hoped would be associated with variation in carboxylase levels. Whilst both enzymes were detected in all genotypes, the levels of activity varied considerably with pod type and with age. In general RuDP carboxylase activity correlated with chlorophyll concentration, and yellow podded types had considerably less activity than green types. The yellow podded genotypes, however, contained significantly higher levels of PEP carboxylase which, in terms of total carboxylase activity, compensated for the lower RuDP carboxylase levels. The activities of both enzymes were determined within the endocarp and within the mesocarp plus exocarp, using 16-day-old pods. All genotypes showed an enrichment for PEP carboxylase in the endocarp and all but one genotype showed a similar enrichment for RuDP carboxylase activity in this layer. The role of the carboxylase enzymes within the pod wall is discussed and it is suggested that their main function may be to maintain an appropriate level of CO2 within the pod cavity as well as recycling carbon to the developing seeds.