Alleviating Effects Of Exogenous NO On Tomato Seedlings Under Combined Cu And Cd Stress

As an important signaling molecule, nitric oxide(NO) is involved in the regulation of resistance to heavy metal stress. By using solution culture, this paper reported the effect of exogenous NO on antioxidase, GSH-PCs synthesis pathways and metallothionein of tomato seedling(Lycopersicon esculentum Mill.) under Cu or Cd treatment.1.Under different copper and cadmium stress, root activity and the activity of NR reduced,content of Cu、Cd increasing in tomato seedling. The application of nitric oxide increased the activity of NR. Under Cu-Cd treatment, exogenous NO decreased the uptake of Cu from root, as well as transportation of Cu into aboveground part, while the transportation of Cd from root to aboveground parts was not changed obviously. Tomato antioxidase system has different sensibility to monometallic exposure and combined exposure to Cu and Cd. Compared with the control, the effect of Cd treatment was a increase of CAT activity, while the main effect of Cu-Cd treatment was a decrease of POD, SOD, APX activity. Exogenous NO increased CAT and POD activity, root CAT activity of tomato under Cu-Cd combined treatment compared. As you can see,a different response and regulation mechanism that involves NO was present in tomato seedlings under Cu and Cd stress. In conclusion, exogenous NO has an influence on enhancement of NR activity and antioxidase enzyme,regulating the endogenous NO metabolic balance and clearing ROS. Compared with CK, total amount of amino acids of root exudates under different Cu,Cd stress was changed in the order of CK>Cu>Cu+Cd>Cd. Adding exogenous NO elevated exudation of total amount of organic acids by root under Cu+Cd stress. The comparative increment of content of organic acid between Cu+Cd and Cu+Cd+SNP treatment was higher than that between Cu and Cu+SNP treatment, Cd and Cd+SNP treatment. Compared with CK,total amount of amino aicds increased under Cd and Cu+Cd treatment, which was benefit to alleviate Cu or Cd phytotoxicity. Adding exogenous NO decreased amount of amino acids under Cd and Cu+Cd treatment, which represent a tendency to get the content level in CK.2.Compared with CK, content of Cu in the subcellular components of tomato root with Cu or Cu+Cd exposure increased significantly. Under Cd exposure, Cd content in subcellular components increased significantly.. Exogenous NO redistributes Cu or Cd content in the different subcelluar components of tomato root under Cu+Cd treatment, as well as enhances the translocation of Cu or Cd into vacuole to alleviating phytotoxicity and regulating cell physiological metabolic balance. Cu treatment decreased glutathione(GSH) concentration significantly. Compared with Cd treatment, the ration of GSH/GSSG under Cu treatment fell by39.8% and 81.6% in roots and leaves, respectively. Exogenous NO could alleviate this inhibiting effect and elevate the ratios of GSH\GSSG under Cu and Cu+Cd treatment in tomato seedlings,keeping a relatively stable redox equilibrium. Compared with CK, the concentration of GSH decreased while γ-glutamyl systeine synthetase(γ-ECS) and GS activities were stimulated in both Cu and Cd exposure, but PCs concentration decreased, which was speculated that growing GSH-PCs metabolic flux increased content of PCs to alleviate combined stress of Cu and Cd.Compared with Cu and Cd single treatment, root PCs content increased under Cu+Cd treatment,which counteract the reduction of leaf PCs content. This stimulated the PCs transportation from root to aboveground part. Under Cu and Cd single treatment, exogenous NO increased concentration of MT significantly, while leaf MT concentration decreased but root PCs concentration increased significantly. MT concentration was higher in leaves than that in roots under Cu+Cd treatment. Exogenous NO may initiate a respond mechanism to stress in leaves and play a major role in alleviating physical damage in combined stress.3. To investigate the effect of nitric oxide(NO) on tomato seedlings root, we analyzed the changes in the metabolic profiles of tomato root exposed to Cu or Cd in a nutrient solution culture system through a targeted GC-MS based technique. In this study, the major metabolite changes were related to amino acid, nucleotide and carbohydrate, in which amino acid take up the highest ratio. After 8d of single metal exposure, the levels of serine, alanine, citric acid, malic acid, lactate acid, fumaric acid, and succinic acid decreased, whereas for Cu+Cd treatment,levels of galactose, isomaltose, and fructose-6-phosphate increased, where glycolysis and TCA cycle present a different metal profile between single metal exposure and Cu+Cd exposure.Following the addition of NO into Cd and Cu+Cd treatment, there was a significant increase in the levels of glycollic acid,glycerol-3-phosphate, glutamine, asparaginate. These results demonstrate the important effect of NO on energy supply, which is required by plant to repiration.