Effects Of Polyamine On Heat Resistance Of Wheat And Its Physiological Mechanism

Object: High temperature stress seriously threatens the growth and yield of crops and is a hot issue in global agricultural production.Wheat(Triticum aestivum L.)is one of the main food crops all over the world,and its production is directly related to the issue of food security.However,in China’s major wheat producing areas,hot weather that exceeds the appropriate grain filling temperature for wheat during grain filling often occurs,which has become the main limiting factor for wheat production.Polyamines(PAs)are organic polycations,which are low molecular weight nitrogen-containing compounds.As a newly discovered plant hormone,polyamine is widely involved in plant growth and development and response to stress.In recent years,more and more studies have shown that PAs are involved in alleviating plant tolerance to various stresses(biological and abiotic).However,physiological studies on exogenous PAs to alleviate wheat grain filling under high temperature stress are relatively rare.Methods: In this study,two spring wheat varieties Xinchun 6(heat-resistant)and Xinchun 31(heat-sensitive)with different heat resistance were used as test materials.At 7 days after flowering,PVC shed was built in the field to simulate high temperature.Exogenous 1mM spermine(Spm)and spermidine(Spd)were sprayed through spike(flag leaf).The changes of grain filling rate,endogenous polyamine(putrescine(Put),Spd and Spm)content,degree of membrane lipid peroxidation(malondialdehyde(MDA)content),antioxidant enzyme activity(catalase(CAT)activity,superoxide dismutase(SOD)and peroxidase(POD),osmoregulation substance content(proline(Pro)and soluble sugar content)and flag leaf photosynthesis and fluorescence characteristics at different stages under four treatments were measured,and the physiological reasons for exogenous Spm and Spd to alleviate the damage of wheat grain filling caused by high temperature stress were explored.Results: 1.After high temperature treatment,the grain filling of xinchun 6 and xinchun 31 was significantly inhibited.Weight of per panicle was significantly decreased by 25% and 32%,respectively.Spraying 1mM Spd and Spm could significantly alleviate the inhibition of high temperature stress on grain filling,and significantly increase the contribution rate of assimilates after flower to grain.HT+Spd significantly increased weight of per panicle of Xinchun6 and Xinchun31 by 5% and 32%,and HT+Spm significantly increased by 19% and 35%,respectively.Under high temperature stress,spraying Spd and Spm significantly changed the contents of endogenous polyamines(Put,Spd and Spm)in flag leaf.HT+Spd significantly increased the Put content of Xinchun6 and Xinchun31,significantly decreased the Spd and Spm content of Xinchun6 and Spm,and significantly increased the Spd content of Xinchun31.HT+Spm significantly decreased the Spm content of Xinchun6 and significantly increased the Put,Spd and Spm content of Xinchun31.2.Under high temperature stress,the net photosynthetic rate and photochemical efficiency of photosystem II of wheat flag leaf decreased significantly.The largest decrease in net photosynthetic rate of Xinchun6 and Xinchun31 occurred in the early stage of high temperature stress,which significantly decreased by 38% and 53%,respectively.At the same time,the water content of leaves decreased.Exogenous spraying of 1mM Spm and Spd effectively alleviated the photosynthetic inhibition of wheat flag leaves,HT+Spd significantly increased the net photosynthetic rate of xinchun 6 and xinchun 31 by 72% and 179% on the 13 d,HT+Spm significantly increased the net photosynthetic rate of xinchun 6 by 22% on the 19 d and 109% of Xinchun31 on the 25 d,which was related to the regulation of antioxidant enzyme activities(SOD,POD and CAT),endogenous polyamine(Put,Spd and Spm)content,osmotic adjustment substance(Pro and soluble sugar content)and MDA content in wheat flag leaves under high temperature stress.3.After high temperature treatment(13 d),the Spm content in grains of Xinchun 6 increased significantly,Put and Spd content did not change significantly,while the Put,Spd and Spm content in grains of Xinchun 31 significantly decreased.SOD,CAT activity and MDA content in Xinchun 6 and Xinchun 31 grains increased significantly under high temperature treatment,Xinchun 6 by 8%,8% and 23% and Xinchn 31 by 13%,8% and 9%.Exogenous Spm and Spd regulated the activities of SOD,POD and CAT,and the content of MDA,soluble sugar and proline in different treatment periods of Xinchun 6 and Xinchun 31 to adapt to high temperature stress,the POD activity of Xinchun 6 and Xinchun 31 at 13 d were significantly increased by 6%,6%,8% and 7%,respectively,Pro content significantly increased at 19 and 25 d,and soluble sugar content significantly decreased at 13 and 19 d.Conclusion: High temperature stress significantly inhibited the grain filling of xinchun 6 and xinchun 31,resulting in significantly reduced yield.Under high temperature stress spraying exogenous Spm and Spd could significantly alleviate the damage of high temperature stress on grain filling of Xinchun 6 and Xinchun 31,and increase yield.