Effects And Physiological Mechanisms Of Different Exogenous Substances On Plant Response To Cold Stress In Wheat

Cold stress is one of the main factors affecting wheat yield and quality.Pretreatment of exogenous substances in wheat production is an operational and convenient way to improve the ability of wheat to cope with cold stress.The response of wheat plants to the late stage of cold stress could be enhanced by spraying different exogenous substances before low temperature.To explore the effects of different combinations of exogenous substances on cold stress tolerance of wheat and its physiological mechanisms,different kinds of exogenous substances were combined into 15 different combinations in this experiment and the research plan was as follows:(1)15 kinds of different exogenous substances were sprayed to explore the effects of different exogenous substances on yield and quality under cold stress before the temperature dropped suddenly at wheat heading stage,and screened out the compound combinations that could improve the cold tolerance of wheat.(2)In order to research the effects of different exogenous substances on the cold tolerance at wheat seedling stage and its physiological mechanism,15 kinds of exogenous substances as those in the field experiment were sprayed before cold stress at wheat four-leaf stage.The main research results are organized as follows:1.Effects and physiological mechanisms of different exogenous substances on cold tolerance in wheat at seedling stageIn order to verify the results of the field experiment,hydroponic experiment was carried out to explore the effects of different combinations of exogenous substances(same as the field experiment)on tolerance under cold stress and its physiological mechanism at wheat seedling stage.Results showed that Q2,Q3 and Q4 treatments also made wheat have stronger cold tolerance.Under cold stress,compared with non-sprayed treatment,Q2,Q3 and Q4 treatments significantly increased the above-ground dry matter weight and the content of chlorophyll,improved photosynthetic rate(Pn),stomatal conductance(GS),maximum photochemical efficiency(Fv/Fm),actual photochemical efficiency(ΦPSII)and photochemical quenching(q P),while non-photochemical quenching(NPQ)decreased significantly.It indicated that Q2,Q3 and Q4 treatments significantly enhanced photosynthetic electron transfer efficiency,leaf photosynthetic rate and dry matter accumulation of wheat under cold stress.Under cold stress,compared with non-sprayed treatment,Q2,Q3 and Q4 treatments significantly reduced the content of reactive oxygen species(ROS)and MDA in wheat leaves,and alleviated the damage of membrane lipid peroxidation caused by cold stress,which was related to the stronger antioxidant enzyme activities(SOD,CAT,APX,GR,DHAR,GPX,MDHAR),higher contents of antioxidants(ASA,GSH)and ratio of ASA/DHA and GSH/GSSG.Activity of antioxidant enzymes in Q2,Q3 was higher than Q4.In addition,Q2,Q3 and Q4 treatments significantly improved the content of osmoregulatory substances with Q4 treatment having a higher content than Q2 and Q3 significantly.It indicated that Q2 and Q3 treatments were more effective in improving the antioxidant capacity of wheat,while Q4 treatment was more effective in increasing the content of osmoregulatory substances in wheat.In conclusion,Q2,Q3 and Q4 treatments were all effective in improving photosynthetic capacity,antioxidant capacity and osmoregulatory capacity under cold stress,thereby increasing biomass accumulation and improving cold tolerance of wheat.2.Effects of different exogenous substances on yield and quality under cold stress at wheat heading stageField experiment was conducted to spray different exogenous substances before low temperature at heading stage.Among the combination of various exogenous substances,the treatments containing "earthworm active peptide solution" as the basic component and betaine(Q2),γ-aminobutyric acid(Q3)or methyl jasmonate(Q4)as the main components were selected to have a good effect against cold stress.Compared with no-sprayed treatment,Q2,Q3 and Q4 treatments significantly increased the chlorophyll content of flag leaf and the above-ground dry matter accumulation of wheat at flowering and mature stage.Among them,Q2 and Q3 treatments could improve the contribution rate of dry matter to grain by promoting dry matter accumulation in various organs,enhancing dry matter translation before anthesis and dry matter accumulation after anthesis,so as to increase wheat yield.Q4 treatment improved thousand-kernels weight and yield by maximizing the contribution rate of dry matter to grain after anthesis and increasing the distribution ratio of dry matter in grain at maturity.After pretreatment with Q2,Q3 and Q4,the contents of total soluble sugar and free amino acids in above-ground organs of wheat increased significantly.The increase of free amino acid content provided sufficient nitrogen source for wheat grain formation at mature stage,thus improving the grain protein content.In addition,Q2,Q3 and Q4 treatments significantly increased grain volume-weight and hardness,wet-gluten content and sedimentation value.Indicated that Q2,Q3 and Q4 treatments could improve grain quality under cold stress at wheat heading stage.