Effects Of Exogenous Application Hemin And Sodium Nitroprusside On Physiological Characteristics And Stress-Resistance Genes Expression Of Salix Matsudana Koidz. Under Cadmium Stress

For a long time,cadmium（Cd）has been widely regarded as one of the major threats to human health.The accumulation of cadmium enters the food chain from soil through crops,which not only affects the normal growth of plants,but also causes serious hidden dangers to human and global dietary health.As an iron-containing porphyrin compound,hemin is the prosthetic group of many proteins such as catalase and peroxidase.Heme oxygenase（HO）can decompose hemin into carbon monoxide（CO）as a gas signal molecule.The HO/CO system composed of the two molecules plays an important role in the process of plant resistance to oxidative damage.Nitric oxide（NO）,as a gas signal molecule,is widely involved in the physiological development process of plants and the response process of plants to stress.Salix matsudana Koidz.belongs to Salicaceae and Salix,is a common tree species in cities.It is a dominant tree species with tolerance to heavy metals and has a good application prospect for soil remediation.In this experiment,through exogenous application of hemin and NO donor sodium nitroprusside（SNP）,one-year-old Salix was used as experimental materials to explore the effects of hemin-related metabolites and NO on the physiological characteristics and stress-resistant gene expression of Salix under Cd stress.Provide a reference for plants to alleviate heavy metal Cd stress and repair soil heavy metal pollution.In this experiment,8 different treatments were set as CK,Cd（75 μM）,hemin（10 μM）,SNP（100 μM）,hemin + SNP,Cd + hemin,Cd + SNP and Cd + hemin + SNP（The concentration of SNP and hemin were obtained by pre-experiment）.On the 7th and 14 th day of the treatment,the morphological indexes of the growth of Salix matsudana Koidz.the physiological indexes in its leaves and the expression of related genes were determined.The results are as follows:1.Under Cd treatment,every part of the growth of Salix matsudana Koidz.was obviously inhibited at d7 and d14,which showed that the height,stem length,root length and leaf area increment all decreased and decreased.Exogenous application of hemin and SNP under Cd stress improved the growth indexes of Salix matsudana Koidz.in different degrees and alleviated the growth inhibition caused by Cd treatment to a certain extent.On the 14 th day of treatment,a large amount of Cd was accumulated in the roots of Salix matsudana Koidz.,and a small part was transported to the stems and leaves above the ground.The single or combined application of heme and SNP increased the accumulation of Cd in the roots of Salix matsudana Koidz.and decreased the transport coefficient of Cd and significantly increased the aboveground bioconcentration coefficient of plants,which effectively increased the accumulation of Cd in Salix matsudana Koidz..2.Reactive oxygen species（ROS）accumulated in large quantities under Cd treatment,the content of hydrogen peroxide（H2O2）and the production rate of superoxide free radicals（O2·-）in the leaves of Salix were significantly higher than those of the control CK in the two periods.The contents of malondialdehyde（MDA）,carbon monoxide（CO）,nitric oxide（NO）,glutathione（GSH）,non-protein mercaptans（NPTs）and the activities of superoxide dismutase（SOD）,catalase（CAT）,glutathione reductase（GR）,ascorbate peroxidase（APX）and heme oxygenase-1（OH-1）all increased significantly,while the content of ascorbic acid（As A）decreased.Under Cd stress,the treatments of hemin and SNP and hemin + SNP reduced the accumulation of active oxygen species in leaves and alleviated the oxidative damage of cells caused by Cd treatment to a certain extent.Cd + hemin + SNP treatment significantly reduced the content of MDA and increased the activity of antioxidant enzymes.Under Cd stress,exogenous hemin and SNP regulated the content of CO and NO in Salix matsudana Koidz.leaves and participated in alleviating the toxicity caused by Cd stress.The application of exogenous hemin significantly increased the contents of GSH and NPTs in Salix matsudana Koidz.leaves under Cd stress,and the tolerance to Cd was further improved.3.Under different treatments,the expression of stress-resistant genes of Salix matsudana Koidz.also changed,Under Cd stress,exogenous application of hemin,SNP and hemin + SNP can upregulate metallothionein gene（MT）,synthase gene（PCS）,transporter gene involved in chelate transport（ABCB）,and nitrate reductase（NR）and nitric oxide synthase（NOS）genes mediating NO production in different degrees during the two periods.The addition of exogenous hemin and SNP is beneficial to increase the formation of chelating agents under Cd stress,regulate vacuole transport genes,compartmentalize Cd complexes,provide more opportunities for effective chelation of Cd ions,and effectively reduce the toxicity brought by Cd.To sum up,the growth of Salix matsudana Koidz.was obviously inhibited after being poisoned by Cd.The antioxidant system is threatened by ROS caused by Cd stress,which leads to serious cell damage.The addition of exogenous hemin and SNP reduced the toxicity of Cd,and the morphological indexes of Salix matsudana Koidz.were significantly improved.Under Cd stress,exogenous application of hemin and SNP promoted the enhancement of antioxidant enzyme activity,caused the increase of non-enzymatic antioxidants and chelating agents,and alleviated the physiological toxicity of Cd to Salix matsudana Koidz..Hemin and SNP also increase the chelation and transport of Cd through genes involved in regulating the synthesis of gas signal molecule NO and genes related to Cd²⁺ chelation and transport,so as to reduce the damage of Cd to Salix matsudana Koidz..