Foliar compound oligosaccharide enhances leaf physiology and key enzyme activities of starch synthesis in winter wheat under mild dry-hot wind stress

Objectives Oligosaccharide, a phytohormone, has anti-stress functions. We studied its effect on resistance of winter wheat to dry-hot wind, to provide a chemical way for controlling dry-hot wind disaster.

Methods A field experiment was conducted in Hengshui, Hebei Province, where winter wheat suffered from dry-hot disaster frequently. Three compound oligosaccharide foliar treatments were set up, as spraying once at jointing stage (BT), once at anthesis stage (HT), and at both jointing and anthesis stage (BTHT), at the same time, tap water (CK) and KH₂PO₄ (CKP) were respectively sprayed at the two stages as controls. At 30 days after anthesis, the flag leaves were sampled for monitoring relative chlorophyll content (SPAD), water loss rate of excised-leaves (RWL), leaf area index (LAI), and the key enzyme activities of starch synthesis; and at harvesting stage, the yield and yield components were investigated.

Results The winter wheat went through two mild dry-hot wind stresses during the experiment. Compared with CK, BTHT increased the SPAD and LAI of winter wheat significantly by 12.36% and 77.78%; BT and BTHT treatments significantly reduced leaf RWL by 15.08% and 21.73% after the first dry hot wind compared to CK, but there were no significant differences between the treatments after the second dry-hot wind; HT treatment increased the ADP-glucose pyrophosphorylase (AGPase) activity by 16.91%, BTHT treatment increased grain starch binding synthase (GBSS) activity by 12.28%, and the soluble starch synthase (SSS) activity by 12.89%. Compared to CKP, LAI was significantly increased by 49.53% to 50.47% under BTHT and HT treatments; HT treatment significantly increased AGPase activity by 14.41%, and BTHT treatment significantly increased GBSS and SSS activities by 6.30% and 9.39%, respectively. Compared with CK, wheat yield was significantly increased by more than 6.69% in all formulation treatments except HT treatment, and wheat thousand grain weight was also significantly increased by 5.09% in BTHT treatment. Under two dry-hot wind stresses, BTHT treatment significantly enhanced leaf physiological characteristics, key enzyme activity in a wheat grain of winter wheat and winter wheat yield compared with the other three treatments. Correlation analysis revealed that GBSS and SSS were significantly and positively correlated with the yield (P<0.05), while the SPAD, LAI, and starch synthase enzyme activities correlated positively with the yield, and RWL correlated negatively with the yield.

Conclusions The BTHT treatment improves the chlorophyll content, water status and starch synthase activity of dry-hot winter wheat. Through the synergistic improvement of starch accumulation and the growth status of flag leaves at the late grain filling stage of wheat, BTHT contributes to the increase in grain weight and mitigation of disaster effect on winter wheat.