Studies On Effects Of High Temperature And Drought On GBSS Activity And Starch Property In Grains And Yield Of Winter Wheat

Two winter wheat cultivars differing in gluten strength, Yumai 34, a strong-gluten cultivar, and Yumai 50, a weak-gluten cultivar, were used in pot culture to investigate the effects of post-anthesis high-temperature stress (HTS) and drought stress (DS) and their interactions on GBSS activity and starch components in grains of winter wheat. Effect of HTS and DS on starch property and PPO actity in the flour and grain yield were also evaluated in this study.The main findings are as follows:1. Activity of GBSS, a key enzyme related to amylose synthesis in wheat grains, increased gradually with the grain filling. It reached the peak around 24-day after anthesis, after which it decreased obviously. Both HTS and drought stress impacted GBSS activity in grains. HTS and DS taken place in the early stage of grain-filling (5 days after anthesis, DAA) and the middle stage of grain-filling (15 DAA) had greater effects on GBSS activity of grain in Yumai 34 and Yumai 50, respectively. No significant interactions of HTS and DS were obtained on GBSS activity in wheat grains in both cultivars, which indicated that consistant effects of HTS on GBSS activity in any soil water contents.2. The results indicated HTS reduced contents of amylose, amylopectin, and total starch in grains of both cultivars. But the responses of starch components in grains in the two cultivars to HTS were different at different grain-filling stages. When suffered fwith HTS, the reduction in amylopectin content in grains of Yumai 34 was relatively greater, especially when HTS taken place in ethe arly grain-filling stage. As for Yumai 50, a relatively greater extent of reduction in amylose content under HTS was observed in the early grain-filling stage. DS led to significant decrease in content of amylose in the two cultivars. But difference responses of amylopectin content to DS were observed between the two cultivars: In the early grain-filling stage, the effects of DS on amylopetin content were not significant in both cultivars. While amylopetin content in Yumai 50 was significantly decreased when DS happen in the middle or late grain-filling stages. However, amylopetin content in Yumai 34 was increased to some extent when suffered from drought stress in the late grain-filling stages. The results also showed significant interactions of HTS with drought on content and components of grain starch in both cultivars, indicating the additive and complicated effects of HTS and DS on wheat starch quality.3. The result indicated that both HTS and DS significantly influenced starch pasting properties. But the two wheat cultivars showed much different dynamic under HTS or DS conditions. DS increased most pasting parameters such as peak viscosity (PV), final viscosity (FV) and hold-through (HT) in Yumai 34, but decreased parameters such as PV, setback (SB) and breakdown (BD) in Yumai 50. HT and FV in Yumai 50 increased in condition of DS in early and middle grain-filling stages, but decreased in late grain-filling stage. HTS increased PV, FV (excluded 5 days after anthesis), SB and BD (excluded 15 DAA) in Yumai 34, but significantly decreased PV, HT and FV in Yumai 50. Analysis also indicated that significant interaction effect of HTS and DS on viscosity parameters existed in both cultivars, which was greater in Yumai 50 than that in Yumai 34.4. HTS reduced flour brightness (L*) in both wheat cultivars. Although the decrease of L * value in Yumai 50 to HTS was greater than that in Yumai 34, no significant difference was observed among the treatments. HTS increased PPO activity in flour in both cultivars, but its effect was small in Yumai 34 than in Yumai 50. The results also showed that the DS reduced flour L * and a * in both cultivars. The influence of DS on a * of Yumai 34 was significant, but not in Yumai 50. DS significantly increased PPO activity in both cultivars.5. HTS reduced grain-filling rate and shortened grain-filling period in both cultivars, which resulted in significant decrease of grain weight and yield. Different influence of HTS was also observed between the two cultivars: HTS in the early stage of grain-filling (5 days after anthesis, DAA) had greater effects on grain-filling rate of Yumai 34, while for Yumai 50, the effect of HTS in the middle stage of grain-filling (15 DAA) was much greater. However, HTS at 25DAA increased increased grain weight slightly in both wheat cultivars. The result also indicated that influence of HTS and DS on Yumai 34 was greater than Yumai 50, indicated that cultivar Yumai 34 was more sensensive to stress. HTS and DS interaction had also a significant influence on grain yield in this pot experiment.