THE EFFECT OF AMINO-ACIDS AND AMIDES ON THE REGULATION OF NITRATE UPTAKE BY WHEAT SEEDLINGS

Wheat plants grown hydroponically increased their nitrate uptake rate more than two-fold after three days of N starvation. Exogenously supplied amino acids and amides had no effect on the nitrate uptake rate of plants well nouriShed in N. After three days of N starvation, however, some of the amino acids and amides supplied to plants inhibited up to 50% of the nitrate uptake rate. The most effective inhibitor was aspartic acid. Asparagine, glutamine or phenylalanine did not show any inhibitory effect. The percentage of inhibition was not increased by increasing the amino acid concentration, nor did the addition of mixed amino acids and amides increase the inhibition exerted by one amino acid alone. During the three days of N starvation, there was a decrease in the concentration of endogenous amino acids in die roots, but not all amino acids decreased their concentration at the same rate. It is suggested that the endogenous levels of some amino acids may repress die nitrate uptake system in plants well supplied with N. During the development of the N deficiency, the concentration of these amino acid decreases, de-repressing the nitrate uptake system.