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Articles

Microbody Enzymes and Carboxylases in Sequential Extracts from C₄ and C₃ Leaves ¹

^a Division of Natural Sciences, University of California, Santa Cruz, California 95060

A seven-step sequential grinding procedure was applied to leaves of Atriplex rosea, Sorghum sudanense, and Spinacia oleracea to study the distribution of carboxylases and microbody enzymes. In the extracts from C₄ species there were 7- to 10-fold reciprocal changes in specific activities of ribulose-1, 5-diphosphate carboxylase and phosphoenolpyruvate carboxylase. No such changes occurred in sequential extracts from spinach. No inhibitors of ribulose-1, 5-diphosphate carboxylase were detected when the mesophyll extracts of Sorghum were assayed together with spinach extracts. These results reaffirm the conclusion of others that phosphoenolpyruvate carboxylase is largely confined to the mesophyll in these species and ribulose-1, 5-diphosphate carboxylase to the bundle sheath. The specific activities of glycolate oxidase and hydroxypyruvate reductase in bundle sheath extracts were two to three times those in mesophyll fractions. Catalase behaved similarly in Atriplex rosea but in Sorghum the specific activity was virtually the same in all fractions. From the relative amounts of these enzymes present, and comparison with the data obtained from spinach, it is concluded that typical leaf peroxisomes are present in the bundle sheaths of both C₄ species and in the mesophyll of Atriplex rosea. The relative enzyme activities in the mesophyll of Sorghum suggest that the microbodies there are of the non-specialized type found in many nongreen tissues. The activities of the microbody enzymes in the bundle sheath of Sorghum seem quite inadequate to support photorespiration.

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