Screening Of Cadmium-resistant Endophytic Bacteria In Callerya Speciosa And The Mechanism Of Alleviating Cadmium Toxicity In The Host

Soil heavy metal cadmium pollution is becoming more and more serious.Cadmium can affect the normal growth and physiological metabolism of medicinal plants,resulting in the decline of the yield and quality of Chinese herbal medicine,and poses a serious threat to human health.It is of great significance for the healthy development of Chinese herbal medicine industry to find a method which can reduce the accumulation of heavy metals in Chinese herbal medicine and ensure the safe yield and quality of Chinese herbal medicine.In this study,a multifunctional endophyte RH5 was obtained from Callerya speciose endophytic bacteria.by measuring the endophytic bacteria RH5 inoculation under different concentrations of cadmium stress on Callerya speciose seedling growth,physiological parameters,cadmium absorption and other indicators.The possible mechanism of promoting plant growth and alleviating the toxicity of heavy metal cadmium provides practical and practical countermeasures for the safe production of Chinese medicinal materials in soil contaminated by heavy metals.The main findings are as follows:(1)13 cadmium-resistant strains were screened from Callerya speciose endophytic bacteria,of which strain RH5 had strong heavy metal resistance and good growth promoting properties.It was identified as Burkhoideria arboris by morphological and 16 S r RNA sequenceanalysis.The bacteria showed resistance to various heavy metals including Cd,Zn,Cu,Mn and Cr.RH5 strain also has excellent growth promoting properties,including nitrogen fixation,phosphorus solubilization,siderophore production,IAA production and ACC deaminase production.indicating that RH5 strain had the potential of heavy metal resistance and plant growth promotion potential.(2)The effects of endophytic bacteria RH5 on vigorous growth and cadmium absorption of Callerya speciose under cadmium stress were studied in pot culture.The results show that RH5 strain could significantly promote the vigorous growth of Callerya speciose.Under cadmium stress,the vigorous growth of Callerya speciose was inhibited,the fresh weight and dry weight of plant roots was significantly reduced,and the development of root systems was hindered.With the increase of cadmium concentration,the absorption and accumulation of cadmium by plants gradually increased,and the growth inhibition effect was more obvious.Inoculation of RH5 strain could increase the root length,number of root tips and root surface area of seedlings roots,promote the growth and development of root systems,and increase the biomass of Callerya speciose root systems.At the same time,RH5 strain can also reduce the absorption of cadmium by plants and alleviate the toxic effects of cadmium on plants.(3)The inoculation of endophytic bacteria RH5 has a positive effect on the photosynthesis of Callerya speciose.With the increase of cadmium concentration,the content of plant chlorophyll(chlorophyll a,chlorophyll b and total chlorophyll content)decreased gradually,and the photosynthesis intensity decreased significantly.At the same cadmium concentration,compared with the uninoculated plants,the chlorophyll content in leaves of the inoculated endophyte RH5 significantly increased,and the net photosynthetic rate(Pn),stomatal conductance(Gs)and other indicators were significantly improved,which promoted the synthesis of chlorophyll and the accumulation of organic matter in plants.Inoculation with endophytes reduced the effect of cadmium stress on seedlings photosynthesis.(4)To study the mechanism of endophytic bacteria RH5 to promote vigorous growth of Callerya speciose and relieve the toxicity of cadmium.The results showed that the inoculation of RH5 strain could reduce the degree of peroxidation of Callerya speciose under cadmium stress,and the contents of MDA and proline were significantly lower than that of the non-inoculated control group.The activities of superoxide dismutase(SOD)and peroxidase(POD)were significantly higher than those of the control group.The above results showed that RH5 inoculation improved the antioxidant capacity of plants and enhanced the tolerance of heavy metals.