1994 journal article

INFLUENCE OF NITRATE ON UPTAKE OF AMMONIUM BY NITROGEN-DEPLETED SOYBEAN - IS THE EFFECT LOCATED IN ROOTS OR SHOOTS

JOURNAL OF EXPERIMENTAL BOTANY, 45(280), 1575–1584.

By: C. Saravitz n, S. Chaillou, J. Musset, C. Raper n & J. Morotgaudry

co-author countries: United States of America πŸ‡ΊπŸ‡Έ
author keywords: AMMONIUM; GLYCINE MAX; NITRATE; NITROGEN, NUTRITION; NITROGEN STRESS; SPLIT-ROOT CULTURES
Source: Web Of Science
Added: August 6, 2018

In non-nodulated soybean [Glycine max (L.) Merrill cv. Ransom] plants that were subjected to 15 d of nitrogen deprivation in flowing hydroponic culture, concentrations of nitrogen declined to 1.0 and 1.4mmol Ngβˆ’1 dry weight in shoots and roots, respectively, and the concentration of soluble amino acids (determined as primary amines) declined to 40ΞΌmol gβˆ’1 dry weight in both shoots and roots. In one experiment, nitrogen was resupplied for 10 d to one set of nitrogen-depleted plants as 1.0 mol mβˆ’3 NH4+ to the whole root system, to a second set as 0.5 mol mβˆ’3 NH4+ plus 0.5 mol mβˆ’3 NO3βˆ’ to the whole root system, and to a third set as 1.0 mol mβˆ’3 NH4+ to one-half of a split-root system and 1.0 mol mβˆ’3 NO3βˆ’ to the other half. In a second experiment, 1.0 mol mβˆ’3 of nitrogen was resupplied for 4 d to whole root systems in NH4+ : NO3βˆ’ ratios of 1:0, 9:1, and 1:1. Nutrient solutions were maintained at pH 6.0. When NH4+ was resupplied in combination with NO3βˆ’ to the whole root system in Experiment I, cumulative uptake of NH4+ for the 10 d of resupply was about twice as great as when NH4+ was resupplied alone. Also, about twice as much NH4+ as NO3βˆ’ was taken up when both ions were resupplied to the whole root system. When NH4+ and NO3βˆ’ were resupplied to separate halves of a split-root system, however, cumulative uptake of NH4+ was about half that of NO3βˆ’. The uptake of NH4+, which is inhibited in nitrogen-depleted plants, thus is facilitated by the presence of exogenous NO3βˆ’, and the stimulating effect of NO3βˆ’ on uptake of NH4+ appears to be confined to processes within root tissues. In Experiment II, resupply of nitrogen as both NH4+ and NO3βˆ’ in a ratio of either 1:1 or 9:1 enhanced the uptake of NH4+. The enhancement of NH4+ uptake was 1.8-fold greater when the NH4+: NO3βˆ’-resupply ratio was 1:1 than when it was 9:1; however, only 1.3 times as much NO3βˆ’ was taken up by plants resupplied with the 1 :1 exogenous ratio. The effect of NO3βˆ’ on enhancement of uptake of NH4+ apparently involves more than net uptake of NO3βˆ’ itself and perhaps entails an effect of NO3βˆ’ uptake on maintenance of K+ availability within the plant. The concentration of K+ in plants declined slightly during nitrogen deprivation and continued to decline following resupply of nitrogen. The greatest decline in K+ concentration occurred when nitrogen was resupplied as NH4+ alone. It is proposed that decreased availability of K+ within the NH4+-resup-plied plants inhibited NH4+ uptake through restricted transfer of amino acids from the root symplasm into the xylem.