Soybean nitrate reductase activity influenced by manganese nutrition

Nitrate assimilation by soybeans [Glycine max (L.) Merrill cvv. Lee and Bragg] was investigated in plants grown in solution culture at manganese concentrations of 0, 1.8 and 275 μM and at day-night temperatures of 33–28° and 22–17°C. Manganese deficiency occurred in plants of both cultivars grown at 0 μM Mn; under these conditions, leaf nitrate concentration increased in both cultivars and nitrate reductase activity in vivo but not in vitro was reduced. High solution Mn (275 μM) produced symptoms of manganese toxicity and reduced nitrate reductase activity of both cultivars in vitro but only of Bragg grown at 22–17°C in vivo. A significant interaction between cultivars and solution Mn concentration was found for in vitro assays for plants grown at both temperatures; this interaction occurred in the in vivo assays for plants grown at 22–17° only.