Effects Of Exogenous Application Calcium And Nitric Oxide On Antioxidant System Activity And Expression Of Related Genes In Salix Matsudana Koidz. Under Cadmium Stress

Due to the rapid development of industry and the extensive use of chemical fertilizers,cadmium?Cd?has become a widespread soil pollutant,which not only inhibits the growth of crops,but also enters the human body through the food chain,causing chronic poisoning.In order to reduce or avoid the adverse effects of cadmium stress on plants,we studied the effects of exogenous application of nitric oxide?NO?and calcium?Ca?on plants under cadmium stress.NO is a stress signaling molecule in plants,it participates in many developmental and physiological processes of plants,including mediating many physiological processes and protecting against metal toxicity.Ca also plays an important role in plant growth and response to various environmental stresses.In this study,by adding NO regulator?NO donor:sodium nitroprusside?SNP?;NO synthetase inhibitor:L-NG-nitroarginine methyl ester?L-NAME??,Ca²⁺and Cd²⁺study the response mechanism of Salix matsudanaKoidzto the three.In this study,Salix matsudanaKoidz was used as experimental material.Nine treatment groups,including control group?CK?,Cd²⁺(100 mg·kg^-1),SNP(75mg·kg^-1),Cd²⁺+SNP,Ca²⁺(2.0g·kg^-1),Cd²⁺+SNP+Ca²⁺,Cd²⁺+SNP+LNAME(70 mg·kg^-1)Cd²⁺+Ca²⁺andSNP+Ca²⁺,were set upto study the effects of exogenous application calcium and nitric oxide on morphological indexes,antioxidant system activity and expression of related genes inSalix matsudanaKoidz.under cadmium stress.The results showed that,?1?Cadmium stress reduced the increment of plant height and leaf area,and SNP and Ca²⁺could alleviate the inhibition.The addition of NO synthase inhibitor L-NAME counteracted the mitigation effect of NO on cadmium,and there was no significant difference in morphological parameters between the two groups.At the same time,due to the addition of exogenous cadmium,a large amount of cadmium accumulated in Salix matsudanaKoidz.Most of the Cd²⁺absorbed by plant roots was stored in roots,in this study,the cadmium content in roots,stems and leaves of Cd²⁺treated plants was significantly higher than that of the control group,and the cadmium content in roots was higher than that in stems,indicating that the cadmium content of Salix matsudana Koidz.under cadmium stress was root>leaf>stem.?2?The content of chlorophyll?chl?in Salix matsudana Koidz.leaves decreased under cadmium stress,and the decreasing extent increased with the prolongation of stress time.Under cadmium stress,exogenous SNP and Ca²⁺treatment increased chlorophyll content and caused a significant increase in growth.Cadmium stress promoted the accumulation of reactive oxygen species?ROS?and cadmiumaccumulation,increased the content of hydrogen peroxide?H₂O₂?and the production rate of superoxide radicals?O₂.^-?.Exogenous application of Ca²⁺andSNP reduced the production of ROS,but the addition of LNAME reversed the mitigation effect of SNP on cadmium stress,suggesting that SNP had a positive effect on Salix matsudanaKoidz.At the same time,cadmium stress increased the content of proline?Pro?.Pro accumulation is one of the important mechanisms of plants responding to cadmium stress.Cd²⁺+SNP and Cd²⁺+Ca²⁺treatment reduced the content of Pro.The contents of malondialdehyde?MDA?in leaves under cadmium stress were decreased by SNP and Ca²⁺treatments,stimulated the activities of enzymatic antioxidants such as superoxide dismutase?SOD?,catalase?CAT?,ascorbate peroxidase?APX?,Monodehydroascorbate reductase?MDHAR?,dehydroascorbate reductase?DHAR?,glutathione reductase?GR?,and so on.The redox balance of cells can be maintained by preventing excessive ROS production.Cadmium stress reduced ascorbic acid?AsA?content and AsA/DHA ratio,increased dehydroascorbic acid?DHA?and glutathione?GSH?.Exogenous application of SNP and Ca²⁺alleviated the negative effects of cadmium stress,enhanced plant metabolism under stress conditions,and alleviated the harmful effects of cadmium stress on plants.?3?The antioxidant enzymes?SOD,CAT,APX,GR?in Salix matsudanaKoidz.leaves increased to varying degrees under cadmium treatment.The up-regulation of CAT and SOD was the greatest,while the down-regulation of these genes under cadmium stress was caused by exogenous application of SNP and Ca²⁺.While the genes involved in plant chelation mechanism?MTs,PCS,ABCB?also increased in varying degrees,of which MT2B and MT1A were the most up-regulation,while SNP and Ca²⁺were applied to reduce their expression.This shows that Salix matsudanaKoidz can eliminate the toxic substances produced by reactive oxygen species and membrane lipid peroxidation by enhancing the activity of antioxidant enzymes under cadmium stress,so as to ensure the normal physiological activities of plants.On the other hand,it can chelate Cd²⁺by synthesizing PCs and MTs,and retain cadmium ions in vacuoles,thus isolating them from other parts of cells,so as to have detoxificationeffect.In addition,exogenous application of SNP mediates NO production and promotes GSH production by increasing the relative expression of NOS?nitric oxide synthase gene?and NR?nitrate reductase gene?,thus alleviating cadmium stress.In summary,cadmium treatment reduced chlorophyll content,plant height and leaf area,while ROS content,antioxidant enzymes,MDA and Pro content in Salix matsudanaKoidz leaves increased in varying degrees.In addition,cadmium stress alsoaffectedtheexpressionofrelatedenzymesgenesinSalix matsudanaKoidz.Exogenous application of SNP and Ca²⁺can alleviate the toxic effects of cadmium stress to varying degrees.