Nitrogen economy of the main shoot of field-grown barley (Hordeum vulgare L.) II. In vivo nitrate reductase activity during growth

Abstract

The method for assay of in vivo nitrate reductase (NR) activity was standardized for barley (Hordeum vulgare L.). NR activity was determined in the various organs of the main shoot of field-grown Jyoti barley at 40 kg N ha^-1. Total nitrate reductase activity (TNRA) of each organ for the period it was metabolically active was calculated. The NR activity was highest in the laminae, followed by the sheaths, reproductive organs; and internodes. The NR activity was high in the first-formed laminae and it showed a decline in the ones formed subsequently. The values varied from 43.2 ± 4.33 to 7.2 ± 1.49 µmol NO^-₃ reduced g^-1 dry wt. h^-1. Maximum TNRA in the laminae, sheath, and internodes was at 49, 84, and 84-93 d after sowing, respectively. The TNRA of the main shoot as a whole showed three peaks, one around 49 d, a second around 63 d, and a third around 84 d after sowing. Correlation coefficient (r) between NR and NO₃ concentration was highly significant in the laminae and sheath viz. 0.76 and 0.62, respectively. The results are discussed in relation to alteration in management practices to maximize nitrate assimilatory activity and the amount of reduced N harvested.