Nitrate Reduction in Roots as Affected by the Presence of Potassium and by Flux of Nitrate through the Roots

Abstract

Dark-grown, detopped corn seedlings (cv. Pioneer 3369A) were exposed to treatment solutions containing$ ext{Ca(NO}_{3})_{2}$, NaNO3, or KNO3; KNO3plus 50 or 100 millimolar sorbitol; and KNO3at root temperatures of 30, 22, or 16 C. In all experiments, the accelerated phase of NO3-transport had previously been induced by prior exposure to NO3-for 10 hours. The experimental system allowed direct measurements of net NO3-uptake and translocation, and calculation of NO3-reduction in the root. The presence of K+resulted in small increases in NO3-uptake, but appreciably stimulated NO3-translocation out of the root. Enhanced translocation was associated with a marked decrease in the proportion of absorbed NO3-that was reduced in the root. When translocation was slowed by osmoticum or by low root temperatures, a greater proportion of absorbed NO3-was reduced in the presence of K+. Results support the proposition that NO3-reduction in the root is reciprocally related to the rate of NO3-transport through the root symplasm.