Fluctuation of enzyme activities related to nitrogen fixation, C6/C1 ratio, and nicotinamide nucleotide contents during soybean plant development

Abstract

Activities of enzymes related to nitrogen assimilation, hexose metabolism, C6/C1 ratios and nicotinamide adenine nucleotide contents were determined in soybean nodules and root tissues during the plant development. Glutamate dehydrogenase and alanine dehydrogenase activities in nodules were more dependent on NADH than NADPH, though the NADPH-dependent activities exhibited higher values in the roots. In both tissues GOGAT activity was NADH-dependent, and G6P dehydrogenase and 6PG dehydrogenase activities were NADP-dependent. These enzyme activities on a mg protein basis showed high levels throughout the plant development and their fluctuations were not correlated with those of nitrogenase activity. Their specific activities, however, exhibited higher values at the early stage of plant development. The C6/C1 ratios in nodule and root tissues were always below 0.6. The value was 0.5 at the early stage, then decreased gradually and increased after the flowering stage. At the early pod filling stage the nodule...