Effect of non-structural carbohydrate accumulation in the stem pre-anthesis on grain filling of wheat inferior grain

To promote the grain weight of wheat, the key is to improve the grain filling of inferior grain. The remobilization of non-structural carbohydrate (NSC) stored in reserve in the stem (sheath + culm) pre-anthesis is important for the grain filling of cereal. However, the mechanism that regulates the NSC reserve in the stem pre-anthesis on grain filling of inferior grains of wheat remains unclear. In the present study, six wheat cultivars with different grain weight were used. Additionally, different rates of nitrogen (N) fertilizer were examined. The objective of the present study was to investigate the relation between the NSC reserve in the stem pre-anthesis and grain filling of inferior grain of wheat and determine the mechanism of that relation. The results showed that the grain weight of inferior grain was significantly lower than that of superior grain, and the inferior grain was more affected by environmental factors than the superior grain. The superior grain had higher content of zeatin (Z) + zeatin riboside (ZR) and activities of synthase (SS) and ADP-glucose pyrophosphorylase (AGPP) and lower rate of ethylene (ETH) evolution than those of inferior grain. Because of these differences, the superior grain had higher sink strength and grain-filling rate and therefore had higher grain weight than that of inferior grain. With a high NSC reserve stored in the stem pre-anthesis, the Z + ZR content increased and the ETH evolution rate decreased in inferior grain significantly, which promoted the sink strength and grain-filling rate of inferior grain of wheat. Suitable nitrogen (N) fertilizer application notably increased the NSC reserve stored in the stem pre-anthesis, which promoted the sink strength and grain-filling rate of inferior grain. However, excess N fertilizer significantly decreased the NSC accumulation in the stem pre-anthesis and inhibited the sink strength and grain-filling rate of inferior grain of wheat.