Abstract:

【Objective】 The present study was carried out to characterize the nitrogen metabolism and activities of the related enzymes during grain filling stage among wheat cultivars differing in protein content. This information will be helpful to elucidate the effects of nitrogen form in source and sink and activities of the related enzymes on the protein content in grains of wheat and will be valuable to wheat cultivation for high quality. 【Method】 Two cultivars from each of the three types of cultivars, the high-, middle- and low-protein content cultivars, were grown in the field of the experimental station of Shandong Agricultural University in Tai’an. The contents of nitrate nitrogen, ammonia nitrogen and activities of enzymes relating to nitrogen metabolism were tested. 【Result】 The protein content of wheat grains showed the change pattern of “high-low-high” during grain filling stage and the protein accumulation in the mature grains was in the order of the high- ＞middle- ＞ low-protein content cultivars. The content of nitrate nitrogen in grain decreased gradually as grain developed, and at maturity, it was in the order of the high- ＞ middle- ＞ low-protein content cultivars. The change of ammonia nitrogen content in flag leaves and grains was similar to that of nitrate nitrogen content in grains. But the ammonia nitrogen content at maturity varied with cultivars. The activities of nitrate reductase (NR) decreased as grains developed, especially, for low-protein content cultivars, the NR activity of which was lower than that of high- and middle-protein content cultivars. The activities of glutamine synthetase (GS) in grains and flag leaves decreased with grains developing in both high- and middle-content cultivars. As for low-protein content cultivars, the change of GS activities in grains was different from that in flag leaves, the later remained the higher value as compared with that of both high- and middle- protein content cultivars.【Conclusion】 It was found that the content of nitrate nitrogen in grains has a significantly positive correlation with activities of NR in flag leaves or GS in grains, also the content of ammonia nitrogen in grains still has a significantly positive correlation with activities of NR in flag leaves or GS in grains and flag leaves. The high- protein content cultivars have stronger ability of supplying nitrate nitrogen for sink from source than middle- and low-protein content cultivars. But low protein content cultivars can make more efficient use of nitrate nitrogen. The high-protein content cultivars with high activities of NR and GS have a stronger capacity of nitrogen assimilation than that of middle- and low-protein content cultivars. The sufficient supply of substrate for protein synthesis is helpful for protein accumulation in wheat grains.

Key words: wheat (Triticum aestivum L.)')">wheat (Triticum aestivum L.), protein content, nitrogen metabolism, enzyme activity