Indole-3-acetic Acid In Leaves Of Plants With Different Arsenic Accumulating Plants Under Arsenate Stress:Speciation,Biosynthesis And Degradation

A previous study showed there was a high indole-3-acetic acid(IAA)level in arsenic(As)hyperaccumulator under As stress.To further study the mechanism of high IAA level in As-hyperaccumulator,a hydroponic experiment was conducted to compare the changes of IAA speciation,synthesis and catabolism in Pteris cretica var.nervosa and Pteris ensiformis under gradient As5+ stress.Moreover,a stepwise regression method was used to study the relationship among determined indices.And then,the indices mentioned above in two plants were detected after cultivating in the condition of low As concentration,with adds IAA synthesis regulators(inhibitor and promoter).The study showed that:1.With the increasing of As5+ concentration,the contents of As and free IAA of two plants increased significantly.At 10 mg L-1 As treatment,As and free IAA contents in P.cretica var.nervosa were 5 and 2 times higher than that in P.ensiformis,respectively.For ester IAA,total ester-IAA and indole-3-acetic acid methyl ester(MelAA)contents of P.cretica var.nervosa increased significantly at 10 mg· L-1 As,compared to control.But those indices decreased significantly in P.ensiformi.s with the increasing of As concentration.Compared to control,the content of 3-indolyl-?-D-glucopyranoside(IAA-Glc)increased significantly in P.cretica var.nervosa at 2-5 mg· L-1 As,and then down to a value,which with no significant difference with control treatment,at 10 mg·L-1 As.However,the trend of IAA-Glc content changed in P.ensiformis was contrary with the former completely.For amide IAA,on the absence of As,the content of total amide IAA accounted for 85%and 51%of total IAA in two ferns.With the increasing of As concentration,total amide IAA and indole-3-acetyl-L-leucine(IAA-Leu)content decreased in P.cretica var.nervosa,but increased in P.ensiformis.The increasing trend of indole-3-acetyl-L-aspartic acid(IAA-Asp)showed in two plants along with the increasing As concentration.However,IAA-Asp content reached 16 ng· g-1 FW in P.ensiformis at 10 mg ·L-1 As,and have no difference with 5 mg· L-1 As treatment.Moreover,the content of IAA-Asp was lower in P.cretica var.nervosa than that in P.ensiformis at all treatment.In addition,there was a significant negative correlation among IAA-Asp content and As,free IAA content in two ferns.It suggested that amide IAA is the main form of IAA in fern,and free IAA played an important role in As accumulation,that was more significant in As-hyperaccumulator.Additionally,As stimulate reversible-amide IAA hydrolysis and ester IAA conjugation to maintain was high free IAA and normal growth in As-hyperaccumulator.2.Arsenic stimulated the increase of tryptamine(TAM)content significantly,but the decrease of indole-3-acetonitrile(IAN)content in P.cretica var.nervosa.However,the contents of TAM,IAN and indole-3-pyruvic acid(IPA)increased in P.ensiformis.In addition,indole-3-acetic acid oxidase(IAAO)activity of P.cretica var.nervosa was lower than that in P.ensiformis in all treatments.There was no significant changes in indole-3-acetic acid peroxidase(IAA-POD)activity of P.cretica var.nervosa,but significant increased in P.ensiformis,with the increasing of As adding.This suggested that the synthesis and degradation of free IAA in As-hyperaccumulation plants were less than As-non-hyperaccumulation under As stress.3.Based on the analysis,free IAA content was positive correlated with TAM content in P.cretica var.nervosa,and negative correlated with IAA-Glc content in P.ensiformis.Furthermore,free IAA contents of two plants were negative correlated with IAA-Asp.It indicated that higher TAM content and lower IAA-Asp content played a crucial role in maintaining high IAA level in As-hyperaccumulator under As5+ stress.4.On the condition of Adding IAA synthesis regulator(inhibitor and promoter),the intensity of IAA biosynthesis was influenced by the significant in two As-stress plants,and further affected free IAA content and As accumulation.IAA synthesis inhibitor significantly decreased TAM,IAN and IPA content in two plants,especially IPA content.Thus,IPA synthesis pathway was the main IAA synthesis pathway in fern.However,TAM synthesis pathway was another main IAA biosynthesis pathway,and more important than others under As(V)stress,because IAA synthesis promoter significantly increased three mediates contents in two plants,especially TAM.In all treatments,the activity of IAAO and the content of IAA-Asp were lower in P.cretica var.nervosa than that in P.ensiformis,indicated that there was a lower IAA degradation ability in As-hyperaccumulator than that in As-non-hyperaccumulator.