Abstract: 【Objective】This study aims to analyze the heredity and gene expression differences of wheat nitrogen metabolism- related indices, which will provide a theoretical basis for selecting wheat cultivars of high nitrogen utilization.【Method】Six wheat varieties with different nitrogen use efficiency and their three hybrid progenies were used as materials which were grown in Hoagland’s nutrient solution with 3 nitrate levels at seedling stage, that are low nitrogen (LN), normal nitrogen (CK) and high nitrogen (HN) at 0.2, 4 and 8 mmol•L-1, respectively. Heredity of morphology, nitrogen metabolism-related enzymes, nitrogen content and nitrogen accumulation in wheat seedling stage and gene expression differences of root and leaf under three nitrogen levels were explored. 【Result】Root length and fresh weight under low nitrogen level were significantly higher than those under normal nitrogen level and their negative heterosis was observed. Seedling height and fresh weight indicating mid-parent heterosis and even super-parent heterosis showed a parabolic trend with the nitrogen level increasing. Root length declined quickly originally and then leveled off with increasing level of nitrogen, while seedling height increased quickly at first and then trended to be stable with the rate of nitrogen increasing. The variation of fresh weight in root and seedling were consistent with root length and seedling height. Nitrogen content of root increased, while that of leaf increased initially and then declined slightly with the rising nitrogen level, nitrogen accumulation as well. Heterosis of nitrogen content in root and leaf was significant under the high nitrogen level. The activity of nitrate reductase and glutamine synthetase was increased with increasing level of nitrogen. Heterosis of nitrate reductase activity was negative, while that of glutamine synthetase activity was positive. Heteroses of nitrate reductase activity and root traits were basically identical, while that of glutamine synthetase activity and seedling traits were mainly consistent. The expression levels of three nitrate transporter genes that performed positive heterosis declined sharply at the beginning and subsequently kept stable with the rising nitrogen level. The expression levels of NRT1.1 and GS1c in leaf all increased at first and then declined with the increasing rate of nitrogen. Their performance of heterosis was positive. The expression levels of NRT1.1 in root showed a substantial increase, while that in leaf decreased significantly under nitrogen stress. Most indices of high nitrogen utilization variety at low N level (YM35) under low nitrogen stress and high nitrogen utilization variety at high N level (DK138) under high nitrogen stress were relatively high. Ten indices of the combination of YM35×DK138 were higher among 15 indices under low nitrogen level, and then 6 and 5 indices were higher under normal and high nitrogen levels, respectively. 【Conclusion】The changing trends of root indices closely related with nitrogen absorption declined quickly at first and then leveled off with the increasing level of nitrogen. The regularity and gene expression levels of these indices related to nitrogen utilization were coincident with which increased quickly originally and then trended to be stable with the rate of nitrogen increasing. Most indices of three crosses showed positive heterosis under three different nitrogen levels. Combination of high nitrogen utilization variety at low N level × high nitrogen utilization variety at high N level was beneficial for breeding of good progeny under the low nitrogen environment. High nitrogen utilization variety for parent mating was beneficial to breed good progeny under the normal nitrogen environment.

Key words: wheat (Triticum aestivum L.) , nitrogen metabolism , heterosis , gene expression , heredity