Mechanisms Of Salicylicacid-mediated Alleviation Of Halosulfuron-methyl Toxicity In Soybean(Glycine Max Merr.)Seedlings

Halosulfuron-methyl(HSM),the sulfonylurea herbicide,is wisely applied in rice and sugarcanefields due to its high efficiency and low toxicity.Thecultivation model of these cropsintercropping with soybeanplayed an important role in development of sugarcane crop in China.Its heavy use and theirresidues may cause negative effects on soybean.Salicylic acid(SA)is amonohydroxy-benzoic acid,which,is well-known signalingmolecule play important roleduring the entire lifespan of the plant.In recent years,research on reducing the toxicity of herbicides has been in the ascendant.Many physiological processes and mechanisms to alleviate the toxicity of herbicide are not known.It is necessary and meaningful to study the process and physiological mechanism of alleviating the HSM toxicity to soybean.It is expected to provide a theoretical basis for reducing soybean seedlings yieldthat caused by HSM residue.The main findings are as follows:1.Exogenous SA alleviates thedecrease in soybean seedlings growth under HSM stress.In the range 0.11-1.0?M,soybean seedlings of dry weight,fresh weight,stem length and root length was decreased with increased concentration when treated with HSM separately.Treated with combined stress of 0.1nM SA and HSM,the decrease of dry weight,fresh weight,stem length and root length would dramatically slow.The results suggested that exogenous Salicylic acid alleviates HSM-induced inhibition of growth through increase in the growth rate,reduce the negative effect of HSM on soybean seedlings thereby.2.Exogenous SA alleviates oxidative stress of soybean seedlings under 1.0?M HSM.The antioxidant enzymes(SOD?POD and CAT)activities,glutathione and antioxidants(GSH)in leaves of soybean seedlings were suffered toxic effects after 1.0?M HSM treatments.SOD,POD activities and GSH content were increased,while CAT activities,which lead to the accumulation of H2O2 and MDA contentsthat compared to control.Treated with combined stress of 0.1nM SA and HSM,the activity of SOD and POD and the content of GSH were markedly increased,and the activity of CAT was reduced that compared to HSM stress,and H2O2 and MDA contents also reduced.The results suggested that exogenous salicylic acid alleviates HSM-induced oxidative stress through eliminating active oxygen radicals,reduce thenegative effect of HSM on soybean seedlings thereby.3.Exogenous SA alleviates the inhibition of photosynthesis of soybean seedlings under 1.0?M HSM.0.1nM SA could improve the photosynthesis coefficient of soybean seedlings under HSM stress,such as Pn,Gs,Ci,Fv/Fm,?PS?,qP and total chlorophyll content and the ratio of Chlorophyll a/b,while it decreased the value of Ls,F0 and NPQ.The results suggested that exogenous salicylic acid alleviates HSM-induced inhibition of photosynthesisthrough promoting both C02 uptake activity and stomatal opening at 1-4d,while at 4-6d mostly through promoting protective reactions to the photosynthetic pigments and maintaining theefficiency of antioxidant metabolism.The study suggested exogenous SA could effectively alleviate the inhibition of HSM stress varieties from the aspects of soybean seedlings growth,oxidative stress and photosynthesis.And mechanisms of SA-mediated alleviation of HSM toxicity to soybean seedlings was revealed.The findings are of great significance to the scientific use and accurate safety evaluation of HSM.