Yield Response of Uniculm Wheat (Triticum aestivum L.) to Early and Late Application of Nitrogen: Flag Leaf Development and Senescence

Nitrogen (N) supply increased flag leaf area by increasing cell number. N promoted initiation and developmentof floret primordia. N availability upto ear emergence affected fertile floret number more than spikelet numberand increased the number of grains. Late application of nitrogen at 5 days after anthesis increased percentagenitrogen in grains, grain weight and grain number due to its effect on ability of floret to set grain. Larger numberof florets and grains provided sink not only for carbon but also for nitrogen accumulation with high nitrogenavailability. The accumulation of grain protein depended on the accumulation and partitioning of reduced Naccumulated during the vegetative stage of growth and the relative contributions of nitrate assimilation and Nredistribution during grain development in low as well as high nitrogen supply. Flag leaf of ‘Gigas’ wheatretained the ability to synthesize RuBPCO on induction of nitrate reductase by substrate supply at post anthesisstage. The reductions in proteolytic enzymes were coincident with loss of Chl, total soluble protein and nitratereductase activity from the flag leaves.