Distribution of nitrate assimilation between the root and shoot of legumes and a comparison with wheat



Legumes of the Phaseoleae (Glycine max L. Merr., Phaseolus coccineus L., P. vulgaris L., Vigna radiata L. Wilczek and V. unguiculata L. Walp.), when grown on 10 mM nitrate, had a low in vitro nitrate reductase (NR) activity in the root compared to the shoot (<15%). In legumes of the Vicieae (Cicer aerietinum L., Pisum sativum L. and Vicia faba L.), Genisteae (Lupinus albus L.) and Trifolieae (Medicago sativa L. and M. truncatula Gaertn.), 30–60% of their total NR activity was in the root. The Phaseoleae had a higher nitrate content in the shoot. Decreasing the nitrate supply increased the relative proportion of NR activity in the root of garden pea (Pisum sativum) and wheat but did not alter the predominantly leaf-based assimilation of nitrate in Phaseolus vulgaris. When in vitro NR activity of the pea shoot was compared with the in vivo NR activity and the rate of accumulation of reduced N by this tissue, similar values were obtained. In vitro NR activity of the wheat shoot was 5 times its in vivo NR activity and 12 times its rate of accumulation of reduced N.