title: Differential effect of amino acids on nitrate uptake and reduction systems in barley roots.
abstract: This study was conducted to determine whether the inhibition of nitrate reductase activity (NRA; EC 1.6.6.1) in barley (Hordeum vulgare L. var. CM-72) roots by the amino acids (glutamic, aspartic, glutamine and asparagine) is a direct effect or indirect due to inhibition of the NO(3)(-) uptake system. Roots of 8-day-old intact seedlings were supplied with the amino acids (I mM) individually either with NO(3)(-) (0.1 or 10 mM) or roots were pretreated with the amino acids and then supplied with NO(3)(-) only. Nitrate uptake was determined by following NO(3)(-) depletion from the uptake solution containing 0.1 mM NO(3)(-). All the amino acids inhibited the increase in NO(3)(-) uptake similarly (50-60%) when the roots were supplied with 0.1 mM NO(3)(-). Pretreatment with glutamic and aspartic acids was more inhibitory (70-80%) than with glutamine and asparagine (30%). The amino acids partially inhibited (35%) the induction of NRA in roots supplied with 0.1 mM NO(3)(-); however, no inhibition occurred at 10 mM NO(3)(-). Likewise, pretreatment with glutamic or aspartic acid inhibited the induction of NRA at 0.1 mM NO(3)(-) but not at 10 mM NO(3)(-). In contrast, pretreatment with glutamine or asparagine had no effect on the subsequent induction of NRA, even at 0.1 mM NO(3)(-). The results suggest that, at low NO(3)(-) supply, the inhibition of induction of NRA by the amino acids is a result of the lack of substrate availability due to inhibition of the NO(3)(-) uptake system.
authors.affiliation: Department of Agronomy and Range Science, University of California, One Shields Avenue, 95616-8515, Davis, CA, USA
authors.forename: M
authors.initials: M
authors.lastname: Aslam
authors.forename: R L.
authors.initials: RL
authors.lastname: Travis
authors.forename: D W.
authors.initials: DW
authors.lastname: Rains