Ureide Metabolism in Leaves of Nitrogen-Fixing Soybean Plants

Abstract

In leaf pieces from nodulated [by Rhizobium sp.] soybean plants, [14C]urea-dependent NH3 and 14CO2 production in the dark showed an .apprx. 2:1 stoichiometry and was decreased to < 11% of the control (12-19 .mu.mol NH3/g fresh wt-1/h) in the presence of 50 mm acetohydroxamate, a urease inhibitor. NH3 and CO2 production from the utilization of [2-14C]allantoin also exhibited a 2:1 stoichiometry and was reduced to a similar extent by the presence of acetohydroxamate with a concomitant accumulation of urea which entirely accounted for the loss in NH3 production. The almost complete sensitivity of NH3 and CO2 production from allantoin and urea metabolism to acetohydroxamate, together with the observed stoichiometry, indicated a path of ureide assimilation (2.0 .mu.mol/g leaf fresh wt-1/h) via allantoate, ureidoglycolate and glyoxylate with the production of 2 urea molecules yielding, in turn, 4 molecules of NH3 and 2 molecules of CO2.