Ectomycorrhizas With Paxillus Involutus Enhance Cadmium Uptake And Tolerance In Populus×Canescens

Ectomyrorrhizas (EMs) are symbiotic organs formed between tree roots and certainfungi,these organs can mediate cadmium (Cd) tolerance of host plants,but the underlyingphysiological and molecular mechanisms are not fully understood.In this study, we used Populus×canescens in combination with or without Paxillusinvolutus to establish mycorrhizal or nonmycorrhizal plants.Afer that,mycorrhizal poplars andnonmycorrhizal controls were exposed to0or50μM CdSO4for40days. Before harvest, fineroots from the plants were selectde for determining net flux of Cd2+by using the Non-invasiveMicro-test Technique. In nonmycorrhizal and mycorrhizal roots of P.×canescens, the600μmfrom the root tip was the maximal Cd2+flux position,besides EMs displayed higher net Cd2+influx than nonmycorrhizal roots. At the same time,net H+flux was determined.The inhibitorexperimentation of plasma membrane was taken by using orthovanadate to determine netCd2+and H+fluxes associated with plasma membrane (PM) H+-ATPases.After that weinvestigated PM H+-ATPases genes HA2.1and AHA10.1as well as the transcript levels ofgenes（ZIP2,NRAMP1.1,PCS,ABCC1,MTP1,ATM3and HMA4） involved in Cd2+uptake,transport and detoxification processes.All these genes were overexpressde in EMs rootscompared to nonmycorrhizal roots. EMs enlarged the total root length, root volume and rootabsorption area, and then mycorrhizal poplars uptook and accumulated more cadmium thannonmycorrhizal poplars. Higher CO2assimilation, improved nutrient and carbohydrate status,alleviated oxidative stress,free proline, soluble phenolics, thiols, ascorbate,glutathione levelsand some enzymatic antioxidants were found in mycorrhizal compared to nonmycorrhizalpoplars.All these changes could enhance P.×canescens Cd tolerance.All these results above indicated that EMs changed the pattern and structure of P.×canescens roots,and enlarge the total absorption area,and increased transcript levels of genes’expression involved in Cd2+uptake and transport,so that the mycorrhizal poplars uptook andaccumulated more cadmium than nonmycorrhizal poplars.And then,EMs could relieve theoxidative stress caused by more Cd uptake and accumulation by improving photosynthesis,nutrient,enzymatic and nonenzymatic antioxidants in mycorrhizal poplars.