The Distribution of some NADP-Linked Dehydrogenases in Photosynthetic Tissues5

Publisher Website
Google Scholar
Abstract
Mesophyll protoplasts of one-month-old maize leaves were separated enzymatically from bundle sheath strands, and purified by centrifugation through a Percoll layer. The protoplasts and BS strands were essentially pure as judged by microscopy, chl a/b ratios, and levels of enzyme markers (PEP carboxylase and NADP-malic enzyme). Chioroplasts were obtained from the protoplasts and from homogenates, and purified through Percoll. The distribution of four NAD P-linked dehydrogenases in tissues and organdies was examined. NADP-triose phosphate dehydrogenasc, used as a chloroplast marker, shows high and comparable specific activities in both main tissues. Glucose 6-phosphate dehydrogenase is located mainly in the mesophyll (at a specific activity of 15.1 μmol h−1 mg−1chl in protoplasts) and is exclusively cytosolic. 6-Phosphogluconate dehydrogenase, also present in both tissue types, has a higher activity in the BS (12.6 in purified strands versus 7.3 μmol h−1 mg−1 chl in protoplasts). It is a cytosolic enzyme, although plastids may contain a low activity. Glyceraldehyde 3-phosphate: NADP reductasc is entirely in the mcsophyll cytoplasm (11.2 μmol h−1 mg−1 chl). It is suggested that the cytoplasm of mcsophyll cells is a site of diversion of sugar phosphates for production of NADPH, at rates, however, compatible with the operation of the triose phosphate shuttle to bundle sheath cells for the synthesis of starch.