Identification And Effectiveness Analysis Of Rice Allelochemicals

Allelopathy is an interference mechanism in which a living or dead plant releases allelochemicals exerting an effect(mostly negative)on the associated plants,which plays an important role in natural and managed ecosystems.In recent years,rice allelopathy has attracted increasing attention as a feasible option for controlling field weeds,since allelopathic rice can reduce weed growth in paddies.However,the composition,the effective concentration and the main source of allelochemicals which released by rice have always been controversial.The key to resolving these problems is to establish a reasonable separation and identification method which could detect the allelochemicals in order to reflect the allelopathic effect exactly,and then to explore the sources of allelochemicals of rice.Thus,rapid and effective analytical methods were developed to study rice allelopathy using modern instruments.The extraction process of allelochemicals was nondestructive.The established methods were successfully applied for the determination of phenolic acids,oxygenic terpenoids and quorum sensing signals molecules.The main results are as follows:(1)Gas chromatography-mass spectrometry/mass spectrometry(GC-MS/MS)method was developed for the determination of oxygenic terpenoids in the hydroponic solutions of rice.The method was rapid and sensitive.Different contents of oxygenic terpenoids were also discussed in the hydroponic solutions of allelopathic rice(PI312777)and non allelopathic rice(Lemont).The results showed that(+)-cedrol can be detected in the hydroponic solution of PI312777 and Lemont.The contents were 2.09±0.07 and 1.52±0.05 ?g/mL,respectively.The contents of(+)-cedrol in the hydroponic solutions of allelopathic rice were significantly higher than that in the non allelopathic rice.(2)Solid-phase extraction(SPE)-high performance liquid chromatography(HPLC)was developed for the determination of 10 phenolic acids(3,4-dihydroxybenzoic acid,phydroxy-benzoic acid,vanillic acid,syringic acid,vanillin acid,ferulic acid,coumarin,benzoic acid,salicylic acid,cinnamic acid)in the hydroponic solutions of rice.At 4-leaf stage,the contents of 3,4-dihydroxybenzoic acid and cinnamic acid were 37.13±0.15 ?g/L and 19.93±0.16?g/L,respectively,in the hydroponic solutions of allelopathic rice,and were 9.34±0.03 and 0 ?g/L,respectively,in the non allelopathic rice.Contents of these two phenollic acids were obviously higher in allelopathic rice than in non allelopathic rice.(3)The proposed methods were used to study the dynamics of oxygenic terpenoids and phenolic acids in the hydroponic solutions of allelopathic rice under barnyard grass stress.The total contents of oxygenic terpenoids and phenolic acids both met their highest level under barnyard grass stress or no barnyard grass stress at 4-leaf stage.At this stage,the contents of(+)-cedrol in allelopathic rice were 1.80 times more than in non allelopathic rice.The concentration was 4.38±0.10 ?g/mL.However,increase of total phenolic acids contents was mainly due to the rapid increase of 3,4-dihydroxybenzoic acid and cinnamic acid.The concentrations were 92.37±0.57 and 20.91±10.17 ?g/L,respectively.On accompanying barnyard grass in the mixed culture solutions,the inhibitory rate of PI312777 on root length,plant height,and plant fresh weight of the target weed barnyard grass were 26.30%,26.18%and 52.74%respectively,they were considerably larger than non-allelopathic rice accession Lemont.In Petri dish bioassay,three allelochmicals can disturb the growth of barnyardgrass under its real concentration,and the anti-barnyardgrass activity was enhanced significantly when two or three allelochmicals were mixed.As mixtures of three allelochmicals were added,the inhibitory rate reached to 59.29%.(4)Poly-glutamic acid modified single-walled carbon nanotube/glass carbon electrode was fabricated firstly by electrochemical polymerization method via cyclic voltammmetry.Then the sensitive layer was prepared by electropolymerization of o-phenylenediamine on above modified electrode in the presence of 3,4-dihydroxybenzoic acid,which acts as a template.Electrochemical sensor of 3,4-dihydroxybenzoic acid based on molecularly imprinted electropolymer exhibited good sensitivity,selectivity,stability and reproducibility.It can be applied to determine 3,4-dihydroxybenzoic acid in rice rhizosphere.(5)A sensitive and rapid method using high performance liquid chromatography/ultraviolet detector(HPLC/UV)method was developed for the determination of quorum sensing sigal molecules acyl-homoserine lactones(AHLs)in rice rhizosphere.3 kinds of AHLs(C10-HSL,C12-HSL and 3-oxo-C8-HSL)were detected and met their highest level in the hydroponic of allelopathic rice under barnyard grass stress.3-oxo-C8-HSL was also detected in fermentation broth of myxobacteria which was separated from the rizosphere of allelopathic rice.