Nitrate reductase activity (NRA) was measured in leaves, stems and roots of six grain legumes supplied with different nitrate concentrations. The contribution of the stem relative to total plant activity was assessed.
In Lupinus angustifolius L., Pisum sativum L. and Viciafaba L., legumes of temperate origin, an increased proportion of total plant NRA occurred in the shoot as nitrate concentration was increased. In Cajanus cajan (L.) Wilisp., Glycine max (L.) Merr. and Phaseolus vulgaris L., legumes of tropical origin, the proportion of total plant NRA in root and shoot was relatively constant regardless of nitrate concentration.
More than 20% of total plant NRA can occur in the stem of G. max, L. angustifolius, Pisum sativum, Phaseolus vulgaris and V. faba. In C. cajan 10 to 15% of total plant NRA was found in the stem at all nitrate concentrations. It is concluded that stem tissues can contribute significantly to overall nitrate metabolism.