| Phosphorus(P)is one of the necessary macronutrient elements for plant growth and development.However,the available P(phosphate,Pi)that can be directly absorbed and utilized by plant roots is deficiency in soil,which limits crop production.Stylosanthes(stylo)is an important legume and green manure crop in tropical and subtropical regions.Screening the high P efficiency germplasm of stylo and researching its mechanism of adapting to lowP stress are of great significance for the genetic improvement of stylo P nutrition traits.In this study,31 genotypes stylo were performed P efficiency evaluation,and the response characteristics of high P efficiency stylo TF291 roots on low P stress were analyzed.The main research results are as follows:(1)The P efficiency of 31 genotypes stylo can be divided into four groups,including P high efficiency and high response group,P high efficiency and low response group,P low efficiency and low response group,P low efficiency and high response group.Thereinto,TF291,TF226,TF234 and TF348 are P high efficiency and high response genotypes stylo,and the growth of TF291 stylo roots was promoted under low P stress.(2)Analysis of root morphology in high P efficiency stylo TF291 showed that the root biomass,total root length,root surface area and root volume of stylo TF291 were significant increased,after 10 or 15 days of low P stress.Subsequently,analysis of expression patterns in expasin encoding genes involved in toot growth,showed that the expression levels of 6 out of 16 expasin genes(SgEXPAl/2/4/8,SgEXPB2,SgEXLB1)were significantly enhanced in TF291 stylo roots.Results indicated that stylo may promote the growth of roots by enhancing the expression of expansin genes under low P stress.(3)Analysis on the acid phosphatase(APase)activity of TF291 stylo roots found that low P stress caused a significant increase of APase activity,accompanied by the expression levels of 4 purple acid phosphatase(PAP)and 3 ribonuclease(RNS)genes increase.The results indicated that under low P stress,stylo roots enhanced APase activity by increasing PAP and RNS genes expression levels,resulted in promoting the utilization of organic P.(4)Analysis of the malic acid content changes in TF291 stylo roots showed that low P caused endogenous malic acid contents significant decrease,but secreted malic acid contents significant increase.Subsequently,expression patterns of Al-activate malate transporter(ALMT)showed that the expression levels of SgALMT2 and SgALMT5 were significantly enhanced under P deficiency.Results suggested that stylo roots promoted the secretion of malic acid by increasing the expression of ALMT genes,thereby enhancing the utilization of insoluble P.(5)Analysis of physiological and biochemical indicators related to the phenylpropane metabolic pathway in TF291 stylo roots showed that the of phenylalanine ammonia lyase(PAL)activity was significantly increased,total phenol and flavonoid were significant accumulations,and total antioxidant capacity(T-AOC)was also significantly enhanced,after subj ected to low P stress.In addition,low P significantly increased the expression levels of two stylo PAL genes(SgPAL2 and SgPAL3)in the roots.Results indicated that the phenylpropane metabolic pathway of stylo participated in the adaptation of roots to low P stress.In summary,there are differences in P efficiency of stylo germplasm resources,and TF291 stylo is a high P efficiency germplasm.TF291 stylo roots adapt to low P stress through a various of physiological,biochemical and molecular responses,including promoting root growth,enhancing malate secretion,increasing APase activity,increasing phenylpropane metabolism and the expression level of related genes.The results of this study preliminarily analyzed the mechanism of stylo roots adapting to low P stress,and laid the foundation for the further cultivation of high P efficient stylo using TF291 as a germplasm material. |
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