Protein Accumulation in Grains of Wheat Cultivars Differing in Drought Tol-erance and Its Regulation by Nitrogen Application Amount under Irrigated and Dryland Conditions

Abstract

The protein accumulation in wheat (Triticum aestivum L.) grains is seldom studied under dryland condition although it has been widely tested under irrigated conditions. For understanding the protein accumulation characteristics of wheat cultivars differing in drought tolerance and the effects of water and nitrogen, a drought-tolerant cultivar, Jinmai 47, and a drought-sensitive cultivar, Nongda 189, were planted under both irrigated and dryland conditions with three nitrogen application rates. From the 5th day after anthesis, spikelets and flag leaves were sampled at a 5 days interval for measuring the contents of protein and its com-ponents in grains and the enzymes activities in grains and flag leaves. The results indicated that the contents of albumin, gliadin, glutenin, total protein, and the ratio of glutenin to gliadin in dryland cropping were higher than those in irrigated cropping, but the globulin content was lower than that in irrigated cropping. For Nongda 189, the contents of protein and its components and the ratio of glutenin to gliadin in grains were affected significently by drought, whereas for Jinmai 47, the variations on contents of globulin, gliadin, total protein, and ratio of glutenin to gliadin were slightly. The activities of glutamine synthetase (GS), glutamate synthase (GOGAT), glutamic acid-pyruvate transaminase (GPT) in grains and the activities of GS and GOGAT in flag leaves were reduced in dryland cropping compared with those in irrigated cropping. Simultaneously, the trend of GPT activity in grains was also affected by dryland cropping. The effect of drought on activities of these enzymes that involved in protein accumulation was greater in Nongda 189 than in Jinmai 47. Nitrogen application promoted the contents of protein and its components in grains, and higher rate of nitrogen application resulted in greater positive effect. Jinmai 47 presented greater effect of nitrogen application on protein content in grains than Nongda 189. Under both growing conditions, the activities of GS, GOGAT, and GPT in grains and the activity of GOGAT in flag leaves in all nitrogen treatments significantly correlated with the protein yield rather than the pro-tein content in grains. The correlation between GS activity in flag leaves and protein yield in grains was different in the two cultivars. The above results suggest that the drought-tolerant cultivar is less affected by water condition compared with the drought-sensitive cultivar; application of nitrogen could promote the protein content in grains, and the effect is greater in the drought-tolerant cultivar than in the drought-sensitive cultivar.