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Keywords:

  • NaCl;
  • Ca2+;
  • N nutrition;
  • N kinetics;
  • Triticum aestivum

SUMMARY

In wheat plants it was found that salinity stress (50 mM NaCl) and an increase in the exogenous Ca2+ supply (to 5 mM) had a differential influence on N uptake capacity depending on the N source (NO3− or NH4+). In NO3supplied wheat plants which had not been supplied with supplemental calcium, a salinity of 50 mM NaCl reduced the N uptake rate of the root by 30 %, reduced the Fmax of NO3 uptake by 38 % and the N concentration of the plants by 35 %. In NH4+supplied plants (which were not affected by a change in calcium concentration) a salinity of 50 mM resulted in a reduction in the N concentration by 16 % (only in the root), a reduction in the Fmax of NH4+uptake by 50 %, while the N uptake rate by the plant was reduced by 16 %. In salt-stressed NO3supplied wheat, an exogenous Ca24 concentration of 5 mM resulted in a 65 % increase in Vmax of NO3 uptake, a 58% increase in NO3 uptake rate by the shoot per g root and a 61 and 5 % increase in shoot and root N concentration respectively. Increased exogenous concentrations of either Ca2+ or K+ had no effect on NH4+ uptake. Kinetic calculations indicate that the inhibitory activity of NaCl on both NO3 and NH4+ uptake was one of noncompetitive inhibition. When NO3, but not NH4+, was the N source, Ca2+ at a concentration of 5 mM partially ameliorated the NaCl-mediated inhibition of NO3 uptake.