The Role Of Arbuscular Mycorrhizal Fungi On The Cadmium Uptake And Accumulation In Upland Rice

Cadmium pollution in rice paddy fields has been reported in many Asian countries such as India,Thailand,and China.Rice?Oryza sativa L.?is one of the most important staple foods in China;however,its cultivation is facing a serious problem of Cd contamination in soil nowadays.Cadmium readily migrates from soil to rice and finally accumulates in grains,thereby entering into the food chain and causing severe damage to human health.Therefore,minimizing Cd in rice grains has become a major public concern wordwide.Arbuscular mycorrhizal fungi?AMF?can form symbiotic associations with the roots of most terrestrial species.It plays a significant role in alleviating heavy metal stress of plants under heavy metal contamination.The development of upland rice production is of great significance to water saving and drought resistance in China.Thus a greenhouse pot experiment was conducted to assess the effects of AMF,Rhizophagus intraradices?RI?or Funneliformis mosseae?FM?on the temporal variation of Cd uptake in upland rice?Oryza sativa L.,Hanyou 3?grown in soil added with 0,2,and 10mg Cd kg^-1,and find out the mechanisms.Our study provides new insights into the role of AMF on Cd uptake by rice and highlights the need for further research on the contribution of AMF under an extensive field study.Results showed that:?1?Both FM and RI mitigated the deleterious impact of Cd on rice growth and significantly improved grain yield in high Cd-contaminated soil(10 mg kg^-1).The Cd concentrations in the grains of mycorrhizal rice cultivated in Cd-contaminated soils(2,10 mg kg^-1)were also significantly decreased,and RI possesses a higher efficiency than FM due to its lower grain Cd concentration.Besides,the significantly lower antioxidant enzymes activities[SOD?superoxide dismutase?,POD?peroxidase?and CAT?catalase?]of the mycorrhizal treatments also confirmed the role of AMF in alleviating the oxidative stress caused by Cd.?2?Root colonization rates fluctuated with growth stages,reaching its peak at jointing stage and then decreasing at flowering and ripening stages.In soil added with 2 mg Cd kg^-1,the concentrations of ethanol and d-H₂O extractable Cd at flowering stage was significantly reduced in mycorrhizal treatments,which may subsequently induce less Cd accumulation in grains due to the positive correlations between ethanol or d-H₂O extractable Cd and grain Cd concentrations at flowering stage.In soil added with 10 mg Cd kg^-1,AMF significantly elevated the proportions of NaCl extractable Cd at ripening stage which may also lead to the reduced grain Cd concentrations,since there was a negative correlation between the percentage of NaCl extractable Cd and grain Cd concentration at this stage.Our study suggested that flowering and ripening stages were important periods for AMF to limit the grain Cd concentrations in rice,when grown in Cd-contaminated soil.?3?The activity of PS?reaction center was inhibited by Cd stress.In low Cd-contaminated soil(2 mg kg^-1),AMF triggered regulatory mechanism to keep photosynthetic electron transport,causing minor damage to PS?activity.In high Cd-contaminated soil(10 mg kg^-1),electron transport was impeded,leading to photoinhibition of photosynthesis.Lower relative mRNA expression of OsNRAMP5 by FM resulted in a decrease of Cd uptake in roots.Besides,RI up-regulated the relative mRNA expression of OsHMA3,prevented the Cd translocation from roots to shoots,leading to the decreasing of Cd in shoots.