Studies on Nitrate Reducing System in Developing Wheat Ears1

Abstract

Developing wheat (Triticum aestivum L.) ears (grains and glumes) are sites of nitrate reduction. Nitrate reduced by the developing ear was incorporated into grain protein. In a field experiment, when no N was supplied, nitrate reductase (NR) activity (µmoles NO2‐/g.f.w./hour) in the glumes and grains was not significantly different from that in the flag leaf blade. Application of N significantly enhanced the NR activity of the flag leaf blade but not that of glumes and grains.Total NR activity (NR activity/g.f.w./hour ✕ fresh weight) of the developing ears equalled that of the leaf blades on the main shoot at low N (0 & 90 kg/ha) levels. At high N (180 kg/ha) level the total NR of the leaf blades was significantly higher than that of the developing ears.In detached culm experiments, flag leaf blade as well as glumes responded to nitrate in the medium even when the detached culms were obtained from plants grown at high N (I80 kg/ha) level. This suggested that under field conditions the enzyme, NR, was operating at sub‐optimal levels. The magnitude of response of glumes was lower than that of the flag leaf blade suggesting preferential flow of nitrate towards the leaf blade or translocational barrier to nitrate movement to the ear.NR activity in the grains was neither enhanced by soil N application nor by additional supply of nitrate to the detached culms.