| Naphthalene（Nap）is a low molecular weight polycyclic aromatic hydrocarbons（PAHs）that is more easily degraded in the soil environment and can be released into the soil through incomplete combustion of organic compounds,waste incineration and industrial activities,causing toxic effects on living organisms.Researchers commonly use phytoremediation techniques to treat PAHs-contaminated soils in situ,with gramineae being one of the plants of choice,and tall fescue,a typical gramineae,has been shown to have the ability to absorb PAHs.In this paper,8-week-old tall fescue roots were firstly exposed to 0,20 and 100 mg·L-1 Nap solution for 9 days to study the toxic effects of Nap on tall fescue,and then the effects of 100 mg·L-1 Nap on the metabolites and metabolic pathways of tall fescue roots were investigated at the metabolic level by high-resolution mass spectrum（UPLC-ESI-HRMS）,aiming to resolve the intrinsic molecular mechanism of interaction between tall fescue and Nap.The main findings of this paper are summarized as follows:（1）Low concentrations(20 mg·L-1)of Nap did not cause toxic effects in tall fescue.However,high concentrations(100 mg·L-1)of Nap caused a significant reduction in the biomass of tall fescue,exhibiting obvious toxicity symptoms such as plant dwarfism and leaf wilting;Malondialdehyde（MDA）content in leaves of tall fescue was significantly elevated,indicating that high concentrations of naphthalene caused oxidative stress to tall fescue leaves;The oxygen evolving complex（OEC）on the donor side of tall fescue photosystem II（PSII）was inactivated,and the actual quantum yield of PSII and chlorophyll content were significantly reduced,indicating that photosynthesis was inhibited.（2）Tall fescue roots were exposed to 0,100 mg·L-1 Nap solution for 9 days in a hydroponic experiment and were sampled and analyzed at 12th hour,3rd day and 9th day,respectively,and were found to cause significant changes in the content of a total of 123 metabolites.It caused stronger metabolic changes in tall fescue roots at 12th hour,and significant up-regulation of IBA and N-Butyryl-L-homoserine lactone expression could promote root growth,indicating that stress mechanisms are rapidly initiated in tall fescue under Nap stress in a short period of time.In addition,the changes in the content of amino acids and derivatives and lipids indicated that the nitrogen pool in the roots of tall fescue is redistributed to interfere with primary nitrogen metabolism in a short period of time,while the changes in the content of alkaloids were the inevitable result of stress in the plant.Notably,a significant upregulation of the expression of 12-OPDA,a synthetic precursor of the phytohormone jasmonic acid,was induced at 3rd day and 9th day,which inhibited plant growth and reduced stomatal opening,and the effect became more pronounced with increasing time.The 100 mg·L-1 Nap solution significantly affected the metabolic pathways of tall fescue roots,and the sphingolipid metabolism,cysteine and methionine metabolic pathways were significantly affected at 12th hour and 3rd day,where sphingolipids play a key regulatory role in plant defense mechanisms,indicating that tall fescue can respond quickly and accurately to defense in a short period of time.The glucosinolate biosynthesis,thiamin metabolism,and purine metabolism were significantly affected at 9th day,indicating that there is a prolonged defense against Nap stress and a complex signal exchange between growth defense and stress response in tall fescue,which regulates the growth of tall fescue under Nap stress. |
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