| The formation of plant allelopathic potential involves in complex rhizosphere microbiological processes that are currently widely accepted by academic communities.The results of some experiments showed that the number of myxobacteria in the rhizosphere soil of PI312777 was significantly higher than the rhizosphere soil of non-allelopathic rice,futhermore,exogenous addition of cinnamic acid and ferulic acid can promote the multiplication of myxobacteria and significantly enhance its allelopathic potential,suggesting that the root exudates of allelopathic rice can promote the growth and aggregation of the bacteria and the bacteria play an important role in rice allelopathy.Rice allelopathic potential is the result of synergistic action of various allelochemicals,In order to reveal the effect of different allelopathic combinations on the growth of mycobacteria in this study,the effects of these allelopathic substances on myxobacteria were studied by adding combination of phenolic acids,combination of terpenoids,combination of phenolic acids and terpenoids.The results are shown that the combination of allelochemicals could promote the growth of mycobacteria at each test concentration,but the effect of combination of phenolic acids was significant,which indicated that the high efficiency chemotaxis and allelopathic induction of phenolic acids.Further the weed-suppression potential on the barnyard grass was evaluated under various induction conditions.The results showed that myxobacteria induced by combination of phenolic acids,combination of phenolic acids and terpenoids could significantly inhibit the growth of barnyard grass than that of the control group,and the inhibitory effect of the combination of phenolic acids on barnyardgrass was the most obvious,and the effect of other combinations was not obvious,suggesting the importance of combination of phenolic acids in rice allelopathy.In the process of induction of allelochemicals,the chemotaxis-related genes that regulate the social behavior of the population of myxobacteria may also undergo corresponding expression changes.To study this change,the total RNA of myxobacteria that induced by combination of phenolic acids,combination of terpenes,combination of phenolic acids and terpenoids in the best induction concentration was extracted,and the expression of chemotaxis-related genes csgA,FruA,FrzCD,csgB,csgG,FrzA and FrzE in myxobacteria were detected by fluorescence quantitative PCR.The results showed that compared with the control group,the above genes were up-regulated induced by combination of phenolic acids,combination of phenolic acids and terpenoids,and the gene expression level was the highest at 3-6 hours.However,the genes have a relatively weak up-regulated expression after 12-24 hours or even 48 hours induced by combination of terpenoids,among them,FrzE gene were down-regulated at different induction time than the control treantment.It seem that the combination of phenolic acids are more likely to promote the expression of chemokine genes in myxobacteria,which can promote the expression of these genes in a short time,and also the the uptake is large.It shows that phenolic acids can regulate the social behavior of the population of myxobacteria effectively.Futher,the fermentation broth induced for 3 hours by different combinations which used,and the growth inhibition rate of barnyardgrass was determined.The results showed that the inhibitory effect of 3 hours of fermentation solution on the stem length of barnyardgrass was significantly improved when chemotaxis-induced combination of phenolic acids,combination of phenolic acids and terpenoids,with the inhibition ratio 23.3%and 23.6%respectively.The inhibitory effect of combination of terpene-induced fermentation broth of myxobacteria and the fermentation broth of myxobacteria on barnyardgrass was not significant,they were only 3.8%and 7.1%.According to the above studies,it is suggested that the myxobacteria can transform these allelopathic substances,in order to reveal the relationship between myxobacteria and allelochemicals,GC-QQQMS was used to analyze the metabolites of Myxococcus Xanthus induced by the combination of allelopathic substances.It was found that after the addition of combination of phenolic acids,combination of phenolic acids and terpenoids,the secondary metabolites of myxobacteria were significantly different in quantity and species in comparison with the control group.It also was found that the effection substances with bioactive was such as querection,therefor we can suggest that Myxococcus Xanthus can interact with phenolic acids and convert them,which may be contribute to improve weed-suppression of myxobacteria.In contrast,the species and quantity of secondary metabolites was not significantly increased when the combination of terpenes add to it.Therefore,in order to verify whether the quercetin has the inhibitory effect,the inhibitory rate of barnyard grass was evaluated by exogenous addition of quercetin.The results showed that quercetin had inhibitory effect on the root length and stem length of barnyardgrass,and the inhibition effect on root length was greater than stem length.It also showed that inhibitory effect was increased by the increase of quercetin concentration.The inhibitory rates of quercetin on the root length were 14.1742%、30.5455%、34.5894%、36.3033%and 60.5901%respectively at the concentrations of 0.32mg/L,3.2mg/L,16mg/L,32mg/L and 160mg/L respectively.In conclusion,this study suggests that the combination of allelochemicals with phenolic acids has a significant effect on the growth and proliferation of myxobacteria with the highest potential for allelopathy.The effect of terpenoids on barnyardgrass was not significant.Phenolic acids can induce the expression of chemotaxis of myxomycetes to promote its growth and proliferation,in addition,phenolic acids can induce myxomycetes produce quercetin with weed-suppression and other compounds,affecting the ability to suppress grass. |
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