The Effect Of Molybdenum Sulfide,nanomaterials Iron Oxide And GABA As Foliar Control Agent Mediated On Cadmium Tolerance Of Chinese Cabbage

In recent years,the rapid development of industry has caused varying degrees of heavymetal cadmium（Cd）contamination in farmland,seriously affecting crop growth and development and then posing a threat to crop production and food safety.Chinese cabbage（Brassica campestris L.）is a typical leafy vegetables and daily edible vegetables that are susceptible to heavy metal contamination.Long-term consumption of cabbage with Cd content exceeding China’s safety standards for leafy vegetables can be hazardous to human health.Foliar control technology has been widely used to reduce heavy metal enrichment in moderately and mildly Cd-contaminated crops because of its ability to enhance crop resistance and control the transport of heavy metals to edible parts of the crop,but there are few highly effective foliar control agents for Cd-stressed leafy vegetables.In this study,molybdenum sulfide（Mo S₂）,γ-aminobutyric acid（GABA）and nano-iron oxide（Fe₂O₃NPs）were selected as foliar control agent to investigate their effect in blocking the enrichment of heavy metals,and the physiological,biochemical mechanisms and molecular mechanisms of Chinese cabbage response to Cd stress mediated by foliar control agent were preliminarily explored by transcriptomics analysis,in order to provide a theoretical basis for the enrichment of efficient and economical foliar control agents and the cultivation and production of Chinese cabbage in Cd-polluted agricultural land.The main test results of this study are as follows:（1）In pot experiment,spraying different concentrations of Mo S₂,GABA,Fe₂O₃NPssignificantly promote that growth of Chinese cabbage,and decreased Cd content,bioconcentration factors（BCF）and transport factor（TF）in edible parts.Spraying 100 mg L^-1 Mo S₂,5 mmol L^-1GABA,and 100 mg L^-1 Fe₂O₃NPs as high foliar control agent had better effect than low concentration on reducing Cd concentration and bioconcentration factor in edible parts of Chinese cabbage,which decreased by 20.25%～40.24%and5.17%～10.27%respectively,and the transfer factor of Chinese cabbage was less than 1.（2）In hydroponic experiment,Cd content in edible part of Chinese cabbage seedling decreased by 43.55%～67.89%by spray high concentration of Mo S₂,GABA and Fe₂O₃NPs which reduces the edible fraction Cd content the most.Spraying three high foliar control agents could effectively enhance the photosynthesis of Chinese cabbage seedlings and alleviate the damage and growth inhibition caused by ROS surge caused by Cd stress.Mo S₂treatment was more beneficial to increase the content of GSH and decrease the content of H₂O₂.GABA was more effective in increasing the activity of peroxidase（POD）and the content of ascorbic acid（ASA）.Spraying Fe₂O₃NPs had better effects on increasing photosynthetic pigment,photosynthetic parameters,activities of catalase（CAT）and ascorbate peroxidase（APX）in edible parts of Chinese cabbage seedlings.（3）RNA-Seq transcriptome analysis showed that differentially expressed genes inducedby spraying high concentrations of the three foliar control agents were mainly enriched in the pathways of photosynthesis,antioxidant system and metal ion transport.The three foliar control agents improved Cd tolerance in plants by inducing up-regulation of photosynthetic system,antioxidant enzymes and genes related to antioxidant substances,and also regulates Cd transport by inducing differential expression of MYB15,ORG3 and Nramp1 genes.It is hypothesized that among three foliar control agents,Mo S₂ up-regulated the expression of more ABC transporter proteins to reduce Cd transport from roots to edible parts;GABA was able to induce up-regulated expression of HIPP24 and HIPP30 genes to regulate Cd distribution in plants,while Fe₂O₃NPs induced the highest levels of HIPP24,HIPP30,MYB15 and ORG3 gene expression.This resulted in a reduction in the Cd content of the edible part of Chinese cabbage.The molecular mechanism by which spray treatments regulate the expression of some pathway genes may be the main reason for the differences in Cd content in Chinese cabbage.（4）The biomass,Cd content in edible part and economic cost of Chinese cabbage sprayed with high concentrations of Mo S₂,GABA,Fe₂O₃NPs were evaluated.The results showed that the fresh weight of Chinese cabbage increased by 2.71～3.01 times than that of CK,the Cd content in edible part decreased by 0.18～0.35 mg kg^-1FW,and the application cost was2.1 thousand yuan,5.8 thousand yuan and 2.3 thousand yuan per hectare respectively.Among them,Fe₂O₃NPs not only has better effect of promoting the growth and reducing the Cd content of the edible part of Chinese cabbage but also has lower cost.This study provides a new way to reduce heavy metal enrichment and safe production of Brassica leafy vegetables.