Photosynthetic Enzyme Activities and Localization in Mollugo verticillata Populations Differing in the Levels of C3 and C4 Cycle Operation

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Abstract
Ecotypic differences in the photosynthetic C metabolism of M. verticillata were studied. Variations in C3 and C4 cycle activity apparently are due to differences in the activities of enzymes associated with each pathway. Compared to C4 plants, the activities of C4 pathway enzymes were generally lower in M. verticillata, with the exception of the decarboxylase enzyme, NAD malic enzyme. The combined total carboxylase enzyme activity of M. verticillata was greater than that of C3 plants, possibly accounting for the high photosynthetic rates of this species. Unlike either C3 or C4 plants, ribulose bisphosphate carboxylase was present in both mesophyll and bundle sheath cell chloroplasts in M. verticillata. The localization of this enzyme in both cells in this plant, in conjunction with an efficient C4 acid decarboxylation mechanism most likely localized in bundle sheath cell mitochondria, may account for intermediate photorespiration levels previously observed in this species.