Physiological response of Piriformospora indica-Medicago sativa symbiotic seedlings to Cd stress
[Background]Cadmium pollution is one of the most serious environmental problems in China due to its strong transferability,resistance to degradation and high toxicity.Phytoremediation can not only absorb and enrich heavy metals,but also reconstruct vegetation,restore landscape,preserve and improve soil and water.The combination of plant and endophytic fungi was used to repair heavy metal contaminated soil in order to promote the function of plant remediation of heavy metal pollution.At present,there are few studies on the responses of Piriformospora indica-Medicago sativa symbiotic seedlings to cadmium,especially the physiological mechanism.The aim of this study is to reveal the physiological characteristics of P.indica-M.sativa symbiotic seedlings in response to cadmium stress.[Methods]M.sativa was used as experimental material to study the response of P.indica-M.sativa symbiotic seedlings to different concentrations of cadmium(0,5,10,30,50 and 100 mg/L)through hydroponic experiments.Then the growth and physiological characteristics,antioxidant activity,and accumulation,enrichment and transfer of heavy metal cadmium of P.indica-M.sativa symbiotic seedlings were analyzed.[Results]Cadmium had a"promotion at low concentration and inhibition at high concentration"effect on M.sativa growth,and this effect was not affected by P.indica.Under the stress of medium and high concentration of cadmium,the inoculation of P.indica helped to increase the biomass of M.sativa seedlings,reduce the number of yellow leaves,and obviously improve their growth condition.2)Under different concentrations of cadmium stress,the physiological indexes of resistance of M.sativa seedlings inoculated with P.indica significantly increased,such as the contents of soluble protein,soluble sugar,proline and antioxidant enzyme activities,and the content of malondialdehyde significantly decreased.3)Inoculation of P.indica increased the bio-enrichment coefficient of M.sativa seedlings,for example,when the concentration of cadmium was 5 mg/L,the bioenrichment coefficient increased by 86.36％compared with that without inoculation.The transfer coefficient of cadmium in M.sativa seedlings decreased by 68.7％when the cadmium concentration was 10 mg/L.[Conclusions]P.indica-M.sativa symbiotic seedlings have strong cadmium tolerance,and the growth status and toxic damage are significantly improved under cadmium stress.Meanwhile,the symbiont seedlings have better cadmium absorption capacity,and mainly accumulate in the roots to inhibit cadmium upward migration.It provides a theoretical basis for the study of microbial-plant stress resistance and the remediation of soil and water pollution caused by heavy metal cadmium.It is of great significance to further strengthen and accelerate the ecological restoration of soil and water conservation.
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