Dynamic Changes Of Phenolic Acids And Its Effects On Specific Microorganisms In Rice Rhizosphere Soil

Using the technology of qRT-PCR the author detected the quantity of Myxobacteria genus and the dynamic changes in phenolic acids released from different allelopathic potential rice accessions in the rhizosphere soil under directly dry-seed sowing and seedling transplanting patterns,meanwhile with specific Myxobacteria species cultured by phenolic acids,this study gave acomprehensive analysis on the relationship among phenolic acids,Myxobacteria genus and allelopathy rice,in order to explore the processes and mechanisms of allelopathic rice rhizobiology,,thus futher provide theoretical supports for field use of allelopathic rice.The main findings are as follows:Under directly dry-seed sowing and seedling transplanting conditions,the trends are similar in the dynamic changing pattern of Myxobacteria ppopulation although the specific microflora differed in the rhizosphere soil at different leaf stages of the same cultivar rice;Between 2-leaf stage to 6-leaf stage of rice,the quantity of Myxobacteria genus was generally PI>Le>PAL-RNAi>CK in order.A small amount of Myxobacteria genus is detected in the soil without rice cultivation.With the growth of rice seedlings after tansplanting,the number of Myxobacteria genus increases in the soil,especially.at the stage showing the stronger allelopathic potential of the tested rice accession,the number of Myxobacteria genus is relatively higher.The results showed that the content of phenolic acids in the allelopathic rice seedlings changed in a "high-low-high" changing pattern in different leaf stages,especially showing higher in 2-leaf,3-leaf and 5-leaf stages,and the content of salicylic acid,benzoic acid,vanillic acid and ferulic acid were relatively rich,which were consistent with the the myxobacteria qRT-PCR test results,revealing that phenolic content was positively correlated to the number of myxobacteria.Further studies showed after interferencing the allelopathic functional gene by using RNAi approach,the total content of phenolic acids released into rhizosphere soil reduced significantly,such as vanillic acid and salicylic acid,however the other species of phenolic acids changed irregularly.Therefore,the authors believed that this situation was not only caused by the metabolic regulation of phenolic acids in allelopathic rice,but also by chemotaxis aggregation and biochemical activities of the specific myxobacteria in rhizosphere soil.The myxobacteria specific aggregation and the allelopathic inhibitory effect on weed were closely related to most phenolic acids exudaated from of root of allelopathic rice into soil.With the method of co-culture experiments using different treatment combinations,we discovered adding different concentrations of exogenous phenolic acids could promote soil Myxobacter proliferation.Between 0?20 ?g/1000 gram soil,the promoting action was significant as added phenolic acid concentrations increased,and showed the highest promoting effect at 20 ?g/1000 gram soi;however added phenolic acid concentration was too low(10 ?g/1000 g)or high(100?g/1000 g),the myxobacteria proliferation effects were poor.Results obtained from the culture medium and sterile-soil cultivation,showed that adding different myxobacterial genus and its fermentation broth were safe and non-toxic to seed germination and its growth of rice tested,but significantly inhibited the target barnyard grass germination and growth,especially the fermentation broth showed the case.Further analysis showed that this results were releated to the allelochemicals existing in the fermentation broth of Myxobacteria,such as Phthalic acid,hex-2-yn-4-yl hexyl ester?BIS(2-Ethylhexyl)phthalate-?5-Hepten-3-one,5-ethyl-2-methyl-?n-Hexatriacontane?1,2-Cyclohexanediol?Nonanamide?2-(1-Cyclohexenyl)ethylamine and 2,4-Dihydroxybenzoic acid etc.From the view of molecular biology and chemical ecology,the research work on the first conducted in field and laboratory conditions at the same time,confirmed that why the allelopathic rice rhizosphere soil aggregats many Myxobacter genus was releated to the phenolic acids released from allelopathic rice accession into the rhizosphere soil,which were used by chemokines myxobacteria for its proliferation,and hence the increased myxobacteria inhibited the target barnyard grass seed germination and growth by both direct infection and the accompanied allelochemical effects.However,it is worth further studying and revealing the rhizosphere biological processes and molecular ecology mechanism how the myxobacteria chemotactically aggregates in the rhizosphere soil of allelopathic rice,in turn exhibits its allelopathic potential in weed suppression.