Effects Of Heavy Metals On The Production Of Siderophores By Trichoderma Asperellum And The Promoting Mechanism Of Siderophores

The increase of heavy metal pollution and salinization in the soil reduced the effective iron utilization in the soil which affected the growth of crops to some extent.Plant rhizosphere probiotics have high development and research value because of that they can produce metabolites such as siderophores to absorb and utilize insoluble iron.Trichoderma asperellum Q1,the plant-promoting fungi was isolated and identified from the soil by our laboratory.It producted high-yield siderophores to respond to abiotic stress and increase crop yield.Due to the pollution of soil heavy metal ions,the effect of soil heavy metal ions on the production of siderophores in the practical application of Trichoderma asperellum Q1 and the role of siderophores of Trichoderma colonization in the plant roots are not clear.The preliminary research findings of our laboratory were that the siderophores of Trichoderma asperellum Q1 can not only transform insoluble iron for plants to absorb,but also promote the content of auxin in Arabidopsis roots,but the specific mechanism is not clear.This paper starts with the identification of T.asperellum Q1 in our laboratory,through the quantitative determination of siderophores under heavy metal ion stress,the growth and infection of lateral roots of Arabidopsis thaliana and the expression of auxin gene in Arabidopsis thaliana roots.In order to further understand the mechanism of promoting the growth of Arabidopsis thaliana and siderophores of T.asperellum Q1,explore the relationship between siderophores and Arabidopsis auxin signaling pathway.The full text results are summarized as follows:(1)The effects of different concentrations of metal ions Al³⁺,Pb²⁺and Cu²⁺on the biomass,siderophores and IAA production of Trichoderma asperellum Q1 were determined.The results showed that the metal ion concentration at the highest siderophores production was 40?mol/L.Al³⁺,100?mol/L Cu²⁺,180?mol/L Pb²⁺.Low concentration of metal ions can induce the production of siderophores and IAA by Trichoderma asperellum Q1 and promote the increase of biomass.When the concentration reached a certain level,the high concentration of metal ions can inhibit the production of siderophores.(2)Trichoderma asperellum Q1,which was screened by rifampicin labeling method,was used to infect the root of Arabidopsis thaliana.It was found that Trichoderma asperellum Q1 could colonize in the root of Arabidopsis thaliana.The colonization number of Trichoderma asperellum Q1 in the media with the siderophores was almost 1.2 times higher than the media which didn't add siderophores,suggesting that the siderophores produced by Trichoderma asperellum Q1 could promote the colonization of mycelia in Arabidopsis root.And there was no significant difference in colonization between insoluble iron and soluble iron,indicating that the transformation of insoluble iron by siderophores improved the iron deficiency stress in Arabidopsis thaliana.The colonization of Trichoderma asperellum Q1 in the insoluble iron medium with siderophores was0.51 times lower than that in the treatment group without siderophores.It is further indicated that the improvement of iron deficiency stress of Arabidopsis by siderophores can reduce the colonization of Trichoderma asperellum Q1.(3)In order to further clarify the relationship between siderophores and IAA secretion in Arabidopsis root and auxin signaling pathway,we used a real-time quantitative RT-PCR(q RT-PCR)analysis to determine the effect of siderophores on root growth of Arabidopsis thaliana based on the proof of that siderophores can promote IAA secretion in Arabidopsis root by using green fluorescent protein gene marker DR5::GFP.The results showed that siderophores could promote the secretion of auxin in the root of DR5::GFP,but did not promote the expression of auxin gene in the root of Arabidopsis thaliana.It was speculated that siderophores couldn't increase the content of auxin in the root of Arabidopsis thaliana by promoting the expression of auxin gene.(4)Trichoderma asperellum Q1 and its siderophores effect on the growth of lateral roots of Arabidopsis thaliana was studied that Trichoderma asperellum Q1 and purified siderophores had significant effect on the root length of lateral roots,but had no significant effect on the number of lateral roots of Arabidopsis thaliana.Studies have shown that iron can accumulate auxin at the top of lateral roots by up-regulating auxin transporter AUX1,thus causing lateral roots elongation without affecting the number of lateral roots.Therefore,it further indicates that Trichoderma asperellum Q1 and its siderophores promotes root growth in Arabidopsis thaliana by promoting the expression of YUC gene.