Study On The Mechanisms Of Exogenous Phosphorus Alleviating The Aluminum Toxicity In Carpetgrass

Carpetgrass[Axonopus compressus（Sw.）Beauv.)]is an important perennial herb in the genus carpetgrass of Gramineae.Carpetgrass displays potential adaptability to acid soils,but its adaptive mechanisms remain largely unkown.Low phosphorus（P）stress and aluminum（Al）toxicity are considered to be important factors inhibiting plant growth in acid soils.Previous studies have found that there is an interaction between phosphorus and aluminum.Phosphorus can effectively alleviate Al toxicity in plants,but there are differences between different plants.Therefore,analyzing the mechanism of phosphorus alleviating the Al toxicity of carpetgrass,investigating Al-responsive genes in carpetgrass root Al-responsive genes can provide candidate gene resources for developing crop varieties with Al tolerance.In this study,effects of P and Al interaction on the root growth and physiological characteristics of carpetgrass genotype‘A58’were analyzed.The study consisted of six treatments:two levels of Al stress as Al Cl₃（0 and 2.1 m M）×three levels of P as KH₂PO₄（0,100,and 500μM）.The gene expression of carpetgrass root in P and Al interaction was analyzed by q RT-PCR;the cloning and expression analysis of Ac MATE1gene were performed.The main results were showed as follows:1.Effects of P and Al interaction on the growth of carpetgrass were analyzed.Results showed under 0μM P treatment,compared with 0 m M Al treatment,the growth of carpetgrass shoot and root were significantly inhibited under 2.1 m M Al treatment,and the dry weight of shoot and root was respectively reduced by 43.5%and 55.8%,and the chlorophyll content and Fv/Fm were inhibited under 2.1 m M Al treatment.However,under2.1 m M Al treatment,phosphorus alleviated the Al toxicity of carpetgrass,especially under500μM P treatment.Under 2.1 m M Al treatment,compared with 0μM P treatment,the total stem length,the leaf number,the shoot and root dry weight and the total root length carpetgrass were significantly increased under 500μM P treatment.Similarly,under 2.1m M Al treatment,compared with 0μM P treatment,the chlorophyll content and Fv/Fm respectively increased by 63%and 23.3%under 500μM P treatment.In addition,under 2.1m M Al treatment,compared with 0μM P treatment,shoot P concentrations、root P concentrations and root Al concentrations of carpetgrass were increased under 500μM P treatment,but shoot Al concentrations was decreased.Results showed the addition of phosphorus can alleviate the Al toxicity of carpetgrass,2.Effects of P and Al interaction on antioxidant system of carpetgrass were analyzed.Results showed that under 2.1 m M Al treatment,compared with 0 and 100μM P treatments,peroxidase（POD）and glutathione reductase（GR）activity of carpetgrass leaf were reduced under 500μM P treatment,but ascorbate peroxidase（APX）enzyme activity and the content of glutathione（GSH）were increased.However,GR enzyme activity and the content of GSH were reduced under 500μM P treatment,but it has no obvious effect on other enzyme activities,indicating that different antioxidant enzymes and antioxidant differently respond to P and Al interaction.3.Effects of P and Al interaction on the activities of enzymes related to organic acid metabolism in carpetgrass and ACP activity were analyzed.Results showed that under 2.1m M Al treatment,compared with to 0μM P treatment,NAD-malate dehydrogenase（MDH）,NADP-malic enzyme（ME）,lemon Acid synthase（CS）and phosphoenolpyruvate carboxylase（PEPC）enzyme activities were both significantly increased under 100μM and500μM P treatment.Similarly,ME,CS and NADP-isocitrate dehydrogenase（ICDH）enzyme activities were significantly increased under 100μM and 500μM P treatment,enzyme activities were increased by more than 14.5%.In addition,without the addition of phosphorus（0μM）,compared with 0 m M Al treatment,ACP activity of leaf and root were significantly reduced by 2.1 m M Al treatment,and ACP activity of leaf and root under 2.1m M Al treatment were both significantly increased by 100 and 500μM P treatments,indicating that enzyme activites related to organic acid metabolism of carpetgrass were enhanced on P and Al interaction.Results showed that phosphorus may participate in alleviating the Al toxicity of carpetgrass by regulating organic acid synthesis and ACP activity.4.Gene expression in carpetgrass roots at different P and Al interaction was analyzed.Results showed that under 2.1 m M Al treatment,compared with 0μM P treatment,the expressions of[Ca²⁺]cyt-associated protein kinase1,phosphate-induced1,acid phosphatase1,multidrug and toxic compound extrusion1,malate dehydrogenase1 gene of carpetgrass root were significantly enhanced in roots of carpetgrass under 500μM P treatment;however,the expressions of ABC transporter 1,NAC domain transcription factor1,NRAT1,SPX1,phosphate transporter1,aquaporin PIP1,auminum-activated malate transporter1,phosphoenolpyruvate carboxylase 1 gene were significantly inhibited in roots of carpetgrass under 500μM P treatment.Results showed that these genes may be involved in the process of phosphorus alleviating the Al toxicity of carpetgrass.5.Clong and expression of Ac MATE1 were analyzed.Full-length c DNA cloning of Ac MTE1 gene were further performed,the full length of Ac MATE1 was 1602 bp,which encoded 433 amino acid residues.Ac MATE1 contained one conserved Mat E domain and nine transmembrane domains.Ac MATE1 was found to be localized to the plasma membrane based on subcellular localization prediction.Quantitative PCR analysis showed that the expressions of Ac MATE1 were enhanced in roots of carpetgrass under both Al and Cd treatments,whereas the expression of Ac MATE1 was inhibited by La treatment.Moreover,the transcripts of Ac MATE1 can be detected in roots,stems and leaves,and Ac MATE1 exhibited the highest expression in the root tip with 0 to 1 cm in length.Results showed that Ac MATE1 may be involved in response to Al toxicity,and part of its functions may be involved in carpetgrass adaption to Al toxicity.Taken together,effects of P and Al interaction on the root growth and physiological characteristics of carpetgrass were analyzed in this study,exploring the physiological mechanism of phosphorus alleviating Al toxicity of carpetgrass.This study provided theoretical basis for In-depth investigating the mechanism of carpetgrass in adaption to Al toxicity.