Effect Of Halosulfuron-methyl On Nodulation And Nodule Nitrogen Fixation Of Soybean

Rhizobium-soybean symbiotic nitrogen fixation of soybean(Glycine Max(L.)Merr.)plays an important role in the growth and development of soybean,which provides large amounts of nitrogen for soybean.Quantity and quality of nodules affect the efficiency of symbiotic nitrogen fixation,and affect the development of plant so as to yield and quality of soybean.As one of sulfonylurea herbicides with high efficiency,high selectivity and low toxicity to mammals,Halosulfuron-methyl(HSM)is widely used in malignant weeds herbicide,cyperus rotundus,etc.At present,the effect of HSM on nodulation and nitrogen fixation of soybean has not been reported,and the effect mechanism is still not clear.Therefore,under the condition of incdoor culture,experiment xwas conducted to explore the effect of HSM to Sinorhizobium.fredii and nodulation,and its influence to the nitrogen fixiation related physiological and biochemical indexes,the results were as follows:1.Inhibitory effect of HSM to rhizobium in vitro was determined in bacteriostatic ring filter method.The results showed that there was no inhibition on rhizobia exposed to HSM with concentration less than 0.50 mg/L.When concertration of HSM reached to 1,5,10 mg/L,the inhition happened,and the bacteriostatic circle diameter under 10 mg/L HSM stress was largest(2.86 mm),with the inhibition rate of 47.67%.2.The inhibitory effect of HSM on soybean nodules was determined with root-irrigation method.The results showed that 21 days after treatment(DAT),inhibition of HSM on total nodule numbers was positively correlated to and the dose of HSM.IC10,IC50 and IC90 were 0.01,0.05,and 0.32 mg/L respectively.As a result,we treated the soybean with concentration of IC10 and IC50(0.01 and 0.05 mg/L)using the same method in follow eaperiment.3.Total nodule numbers,dry weight of nodule and shoot were inhibited under HSM stress.Compared to the control,the inhibition of 0.01 mg/L HSM to total nodule numbers were not significant,but it was significantly with 0.05 mg/L HSM treatment,and the maximum inhibition rate was 44.53%at 35 DAT.Dry weight of shoot and nodule was significantly inhibited.The maximum inhibition rate happened at 35 DAT with the inhibition rate of 49.46%and 48.15%respectively.However,there was no obvious inhibition of root dry weight,on the contrary,0.01 mg/L of HSM increased the root dry weight.4.There was no significantly effect of HSM on the microstructure of nodules.Compared to the control,the nodules exposed to 0.05 mg/L of HSM growed more parenchyma cells among infected cells in infection zone,and most of infected cells loosely arrange.5.The effect of HSM on total nitrogen,soluble protein and leghemoglobin content of soybean plant and nodule.There were obvious inhibitory effect of HSM with concentration of 0.05 mg/L on total nitrogen content and soluble protein content of root and leaf,but the inhibitory effect reduced with the extension of time.However,0.01 and 0.05 mg/L of HSM had no negative effect in nodule.In addition,HSM has inhibitory effect on bean leghemoglobin content in nodule,with inhibition rate up to 40.86%in 21-35 DAT.6.The effect of HSM on nitrogenase,glutamate synthetase and glutamine synthetase.HSM significantly inhibited the activity of nitrogenase,which the maximum inhibition rate of 0.05 mg/L of HSM was up to 34.15%in 21 DAT.There was no significant effect of HSM on glutamate synthase of shoot,but activated glutamate synthetase activity of root and nodule treated with 0.05 mg/L of HSM,which the most significant effect in 28 and 35 DAT.HSM inhibited the of glutamine synthetase activity of soybean leaf and nodule with inhibition rate of 19.66%and 69.76%,respectively.But HSM activated glutamine synthetase activityThe results clarified the effect of HSM on nodulation and nitrogen fixation of soybean,and preliminary discussed the mechanism of it,which was of great significance in further investigating the phytotoxicity and its mechanism of halosulfuron-mcthy on symbiotic soybean.