Activities of Principal Photosynthetic and Photorespiratory Enzymes in Leaf Mesophyll and Bundle Sheath Protoplasts from the C_3-C_4 Intermediate Flaveria ramosissima

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Mesophyll and bundle sheath protoplasts were differentially isolated for the first time from leaves of a C_3-C_4 intermediate, Flaveria ramosissima. Protoplasts were partially purified from leaf digests following differential centrifugation and flotation on dextran step-gradients. Two mesophyll and one bundle sheath fraction were obtained, with relative purities of the preparations determined visually as >95% for mesophyll and >80% for bundle sheath. Representative C_3 and C_4 photosynthetic enzymes had substantial activities, on a chlorophyll basis, in all three protoplast preparations. The activity of phosphoenolpyruvate carboxylase was highest in the lower density mesophyll fraction and lowest in the bundle sheath fraction. Conversely, the activity of NADP-malic enzyme was highest in the bundle sheath, and lowest in the lighter mesophyll preparation. Ribulose 1,5-bisphosphate carboxylase/oxygenase had similar activity in all three preparations, as did glycolate oxidase. However, glycine decarboxylase was about 3-fold enriched in the bundle sheath fraction. The data indicate that the partial compartmentation of photorespiratory metabolism may contribute along with limited C_4 photosynthesis to reducing photorespiration in this intermediate species.
日本植物生理学会の論文