Effect of Nitrogen on Grain Filling of Wheat and Its Physiological Mechanism

In order to know the influence and physiological mechanism of nitrogen( N) application on wheat grain filling,two local high-yielding wheat varieties,Yangmai 16 and Ningmai 13,were grown in field,and 120kg·hm- 2(LN),180 kg·hm- 2(MN) and 240 kg·hm- 2(HN) were applied during the whole wheat growing season. Grain filling level of superior and inferior grains and changes in activities of key enzymes involved in sucrose-to-starch conversion in grains were determined. The results showed that grain yield was increased with the increase of N level,but it exhibited no significant difference between MN and HN. Nitrogen partial factor(grain yield /N amount) was significantly decreased with the increase of N level. When compared with LN,the activities of adenosine diphosphoglucose pyrophosphorylase( AGPase),soluble starch synthase( SSS) and starch branching enzyme( SBE),grain filling rate and grain weight of inferior grains for Yangmai 16 increased with MN treatment,while decreased with HN treatment. The enzymatic activities,grain filling rate and grain weight of inferior grain were decreased with the increase of N level for Ningmai 13. No significant effect of Nlevel on the grain filling of superior grains was detected. The results indicated that N level mainly regulated grain filling of inferior grains,and the regulation varied with varieties. The grain filling rate and grain weight of inferior grains are closely associated with the enhancement or reduction in activities of the key enzymes in sucrose-to-starch conversion in these grains. Under good soil fertility,high yield and N use efficiency could be achieved when N level was 180 kg·hm- 2.