Study On The Cadmium-induced Physiological Response And Enrichment Performance Of Salix Matsudana Koidz With The Assistance Of Microorganism

Phytoremediation is a low cost and environmentally friendly solution to Cd contamination.However,as a non-essential element of plants,Cd may interfere with plant growth.Plant growth-promoting bacteria is expected to further enhance the tolerance and enrichment to Cd of plants because of its various growth-promoting traits.Salix matsudana Koidz is a widely distributed Salix sp.,which could be an ideal material for mitigating Cd contamination,due to its high accumulation capacity,large biomass,rapid growth,and quick expansion of root.Sphingomonads exist widely in the environment and are often used as auxiliary means to improve the phytoremediation efficiency.Therefore,this study uses S.matsudana as a plant carrier and uses a hydroponic experiment to elucidate the detoxinization and enrichment strategies of S.matsudana that cope with different concentrations of Cd?0?mol/L?Control?,25?mol/L?Cd25?,50?mol/L?Cd50?,and 75?mol/L?Cd75??,in terms of growth performance,cell wall polysaccharide remodeling,and antioxidant stress.This study also investigate the regulation pathway of microorganism to the Cd tolerance and accumulation strategy of S.matsudana by inoculating endophytic bacteria Sphingobium yanoikuyae Sy310 in plant.The main results were summarized as follows:1.S.matsudana roots posed high enrichment ability and tolerance to Cd.The results showed that about 68.45%?84.46%of Cd content was retained in roots.Cd tolerance of roots were higher than that of shoots,displaying with shoot dry weight under Cd treatment was significantly lower than that of control?p<0.05?,while the root dry weight under Cd75 treatment was significantly lower,compared to control?p<0.05?.In the presence of Cd,root length decreased significantly?p<0.05?,and root morphology change contributed to the reduction of Cd absorption.Cd regional sequestration in the root cell walls is essential for Cd enrichment and protection of protoplasts,and cell wall polysaccharides play important roles.Cd content in the root cell walls is about 26.98%?63.47%of that in roots.Under Cd treatment,pectin content and pectin methylesterase?PME?activity in the root cell walls were significantly increased?p<0.05?,indicating that more-COOH could bind to Cd.In addition,the contents of hemicellulose 1?HC1?and hemicellulose 2?HC2?increased significantly to different degrees under Cd stress?p<0.05?,indicating that the number of negatively charged groups?such as–OH?improved.2.Cd induced the disorder of redox reaction in S.matsudana,exhibiting by the contents of H₂O₂,O₂^-and malondialdehyde?MDA?in leaves increased?p<0.05?,and root H₂O₂ and MDA contents enhanced significantly,compared to control?p<0.05?.S.matsudana have a well-developed antioxidant system to cope with Cd-induced oxidative stress.Under Cd stress,peroxidase?POD?activity and glutathione?GSH?contents in leaves and roots were significantly increased to different degrees?p<0.05?,and superoxide dismutase?SOD?activity in roots and leaves was significantly higher than that of control?p<0.05?.Catalase?CAT?activity was sensitive to Cd,and CAT activity was significantly decreased under Cd treatment,compared to control?p<0.05?.3.A microbial acclimatization experiment was carried out by using a series of streptomycin concentrations and finally obtained a strain with a tolerance of 300?g/m L streptomycin,and named it Sy310.The 16S r DNA sequences of Sy310 were analyzed by multiple sequence alignment and genetic relationship.The results showed that Sy310was Sphingobium yanoikuyae.Sy310 was a gram-negative bacteria,streptomycin and Cd50 treatment had no significant effect on its morphology and auxin?IAA?production?p>0.05?.Streptomycin had no significant effect on the growth curve of bacteria,while Cd inhibited the growth of Sy310,showing delayed logarithmic and stationary phases,and decreased bacterial count in stationary phase?p<0.05?.4.The Sy310 inoculation significantly enhanced biomass and root length of S.matsudana?p<0.05?,as well as alleviated the inhibition on growth in the presence of Cd.This may be associated with the increased root IAA content in the presence of Sy310?p<0.05?.Sy310 significantly increased Cd accumulation in roots?p<0.05?.Cd content in root cell walls in the presence of Sy310 was 53.07%higher than that in Cd treatment only?p<0.05?.Sy310 enhanced the synthesis of pectin,HC1,and low methyl-esterification level of pectin in cell walls under Cd stress.Transmission electron microscope image of root tips showed that the cell wall in Cd50+Sy310 treatment was thicker than that in Cd50 treatment.Increased Cd binding sites and reduced porosity due to thickening of cell walls may facilitate Cd regional sequestration.In addition,Sy310 did not induce cell wall polysaccharides remodeling and cell wall thickening in the absence of Cd.5.The Sy310 inoculation alleviated Cd-induced oxidative stress,and the contents of H₂O₂,O₂^-and MDA in leaves in Cd50+Sy310 tratment were significantly lower than that in Cd50 treatment?p<0.05?.Compared with Cd50 treatment,H₂O₂ and MDA contents in Cd50+Sy310 treatment remained at a lower level?p<0.05?.Sy310 increased CAT activity in leaves and roots under Cd stress?p<0.05?.POD and SOD activities and GSH content in leaves treated with Cd50+Sy310 were significantly decreased compared with those in Cd50 treatment?p<0.05?,indicating that Sy310 alleviated Cd-induced toxic reaction,and kept oxidative stress at a relatively low level.To sum up,this study demonstrated that S.matsudana could cope with Cd stress by changing root morphology,remodeling root cell wall polysaccharides and improving antioxidant capacity.Endophytic bacteria Sy310 was able to regulate the growth performance,the remodeling of polysaccharides in root cell walls and the level of oxidative stress in S.matsudana under Cd stress,thus improving the tolerance and enrichment ability of S.matsudana to Cd.