Enhancement of Glucose Utilization in Provision of Carbon Skeletons for Ammonium Assimilation in Wheat Roots

In providing carbon skeletons to be expended for amide synthesis during ammonium assimilation, glucose utilization in roots was studied. The roots of young wheat plants grown without nitrogen for 3d and grown with 4 mM NO_3^- or NH_4^+ for 1d were fed with ^<14>C－glucose for 3h in the presence of NO_3^- or NH_4^+, and the distribution of ^<14>C-metabolites within the plants was examined. The NH_4^+ supply changed the distribution of ^<14>C to a greater extent than the NO_3^- supply. In roots grown with NH_4^+ for 1d, the incorporation of ^<14>C into 80% ethanol-soluble materials in roots increased, and the ratio of ^<14>C in basic metabolites to ^<14>C in acidic metabolites in the fraction was high. The concentration and ^<14>C-labeling of citrate and malate in roots were reduced by the prolonged supply of NH_4^+. In contrast, the asparagine concentration conspicuously increased, and asparagine was heavily labeled in roots of NH_4^+-grown plants. When roots were treated with methionine sulfoximine, however, ^<14>C-labeling of basic metabolites did not increase despite the supply of NH_4^+. These results indicate that the supply of NH_4^+ has a stimulatory effect on the degradation of glucose in wheat roots to provide carbon skeletons necessary for amide synthesis during NH_4^+ assimilation