The localization of nitrate-assimilating enzymes in leaves of plants with the C4-pathway of photosynthesis

Abstract

The vascular bundle of leaves with the C4-pathway of photosynthesis is usually surrounded by two concentric chlorophyllous cell layers: an outer mesophyll layer and an inner bundle sheath layer. The localization of the nitrate-assimilating enzymes, nitrate reductase, nitrite reductase, and glutamate dehydrogenase in Zea mays, Gomphrena globosa, and Sorghum sudanense was studied by differential grinding. Nitrate reduction to nitrite appears to occur primarily in mesophyll cells. The nitrate content of the mesophyll cells was much higher than the nitrate content of the bundle sheath cells. The distribution of nitrite reductase seemed to be related to the presence of chloroplasts with grana. Ammonia incorporation into organic compounds by glutamate dehydrogenase was localized in the bundle sheath cells.