Tissue and cellular localization of NADH-dependent glutamate synthase (NADH-GOGAT, EC1.4. 1.14) in young leaves of dicotyledonous spinach (Spinacia oleacea) was investigated using the immunocytological method with an affinity-purified anti-NADH-GOGAT immunoglobulin G. Immunoblotting analysis showed this antibody specifically cross-reacted with NADH-GOGAT protein in crude soluble proteins from young leaf blades of spinach. When transverse sections (10μm in thickness) prepared from the paraffin-embedded young leaf blades of spinach were stained with the anti-NADH-GOGAT antibody, strong signals for NADH-GOGAT protein were detected in companion cells of large vascular bundles. Weak signals for the NADH-GOGAT protein were also detected in vascular parenchyma cells and mesophyll cells of young leaves. Ferredoxin (Fd)-GOGAT (EC 1.4.7.1) protein was mainly located in mesophyll cells and signals for the protein were also detected in companion cells and xylemparenchyma cells of large vascular bundles. By the way, in young leaf blades of monocotyledonous rice, NADH-GOGAT protein specifically located in vascular cells and Fd-GOGAT protein was abundant in mesophyll cells (Hayakawa et al., 1994). The differences of functions in young leaves for NADH-GOGAT proteins between monocotyledonous rice and dicotyledonous spinach are discussed
