Intracellular Localization of Phosphoenolpyruvate Carboxykinase in Bundle Sheath Cells of C<sub>4</sub> Plants

Abstract

Bundle sheath protoplasts (BSP) were isolated and purified from four C4 species of the phosphoenolpyruvate (PEP) carboxykinase type (Panicum maximum, P. texanum, Chloris gayana and Eriochloa borumensis), and cell organellses were separated from the BSP extract by differential centrifugation or sucrose density gradient centrifugation. Separation of the organelles was ascertained by the distribution of marker enzymes for chloroplasts, mitochondria, peroxisomes and cytoplasm. Contrary to the previous report [Rathnam and Edwards (1975) Arch. Biochem. Biophys. 171: 214], the distribution of PEP carboxykinase in BSP of P. maximum was the same as that of UDP-glucose pyrophosphorylase, a marker for cytoplasm, and PEP carboxykinase activity was not recovered in the intact chloroplasts. The same results were obtained with P. texanum, C. gayana and E. borumensis. Therefore, we conclude that PEP carboxykinase is exclusively localized in the cytoplasm of bundle sheath cells of C4 plants.