Abstract:

In order to understand the effects of soil water availability on nitrogen assimilation enzyme activity and grain quality in winter wheat cultivar, pot experiments were carried out at the Henan Agricultural University Research Station during 2001-2003. Soil containing 9.8 g•kg-1 organic matter, 0.986 g•kg-1 total N, 25.43 mg•kg-1 olsen-P and 259 mg•kg-1 NH4OAc-K were used for the experiments. 18 kg of sieved soil was placed in each 30 cm × 40 cm pot. ‘Yumai 34’, a strong gluten cultivar, was used in the experiments. Three water treatments were used: soil water content of 60% field capacity (FC), 40% FC and 80% FC. All pots were under a rain-shelter, and water levels were controlled from elongation stage to harvest. Water content was measured by weight every two days. Before sowing, 3.5 g N, 3.3 g K2O and 2.9 g P2O5 were applied to each pot and a further 1.6 g N was applied to each pot during the elongation stage. Seven plants from each pot were selected when plants had five leaves. The experiment was arranged in a completely randomized design with ten replications per treatment, and all pots were managed in the same way. The results indicated that nitrate reductase (NR) activity in the flag leaf declined after anthesis in a decreasing order of 60%FC >40%FC >80%FC. Glutamine synthetase (GS) activity in both the flag leaf and grain all declined from the beginning of anthesis to 15 days after anthesis and then increased with the order among the three water treatments as follows: 80%FC＞60%FC＞40%FC. A similar pattern was found for glutamate synthase (GOGAT) as for GS. The highest grain yield and the best nutritional quality occurred in the 60%FC treatment whereas the 80%FC treatment had the lowest quality and 40%FC had the lowest grain yield. Grain protein content was positively correlated to NR and GS activity in flag leaves and GOGAT activity in the grain, and was negatively correlated to GOGAT activity in the flag leaves for all water treatments. In the 40%FC and 80%FC treatments, there was a significant correlation between grain protein content and GS activity in flag leaves. In the 60%FC treatment, there were significant correlations between grain protein content and NR activity in flag leaves and GS activity in grain, and grain protein was closely correlated to GS activity in flag leaves.