Study On Exogenous Glutathione Mediated Nitric Oxide To Regulate Salt Adaptability Of Tomato Seedlings

Tomato is an important vegetable cultivation crop in facility,it is sensitive to moderate salt.Therefore,the phenomenon of soil salinization has become an obstacle to the tomato plant to achieve high yield,high quality and high efficiency in facilities.This experiment used hydroponic methods to imitate soil salinization in natural environment.The tomato variety?Zhongshu No.4‘was served as the test material To study the relationship between exogenous glutathione?GSH?and nitric oxide?NO?signaling molecules in the regulation of tomato seedlings'response to salt stress.The main results were presented as follows:1.Compared with the control,the NaCl treatment was significantly decreased NO content,nitrate reductase?NR?and nitric oxide synthase?NOS?activity in leaves of tomato seedlings.Compared with the NaCl treatment,NaCl+GSH treatment significantly increased NO content and NR activity in leaves,but the NOS activity had no significant effect.NaCl+Hb treatment significantly reduced NO content at 24 h and 72h,but the NR and NOS activities had no significant changes.Compared with NaCl+Hb treatment,NaCl+Hb+GSH significantly increased NO content during the whole treatment period and NR activity at24 h and 48 h,and NOS activity at 48 h and 72 h.The results showed that Hb could reduce the content of endogenous NO in leaves.However,exogenous GSH could induce endogenous NO synthesis by promoting NR and NOS activity,and thus slowed the damage caused by salt stress to plants.2.Compared with the control treatment,NaCl stress significantly increased the activities of roots as well as the contents of proline,soluble sugar and the contents of Na⁺,Cl^-and S^2-?at 24 h?in leaves of tomato,decreased the contents of NO,Ca²⁺?except 24 h?,K⁺?at 24 h?and the activities of NR and NOS at24 h after treatments.Compared with NaCl treatment,NaCl+GSH significantly improved root activity?at24 h?and the contents of soluble sugar?except 48 h?and S^2-,as well as increased the NO content and the activity of NR,but decreased the contents of Na⁺and Cl^-at 72 h after treatments;NaCl+Hb significantly increased root activity?at 24 h?and the contents of proline?except 24 h?,soluble sugar,and Cl^-at 72 h after treatments,but declined the NO content.Compared with NaCl+Hb treatments,NaCl+Hb+GSH increased the activities of roots,NOS?except 72 h?,and NR.Meanwhile,it increased the contents of NO and S^2-?except 48 h?.It shows that,salt stress reduced endogenous NO leaves by inhibited the key enzymes of NO,broke intracellularion balance,and the radio of intracellular Na⁺/K⁺and Na⁺/Ca²⁺was large.While aggravated the damage of salt stress on plant,Hb caused cells to maintain higher osmotic potential to respond to stress.These results showed that exogenous GSH can induce the increase of endogenous NO and intracellular inorganic S^2-,while inorganic S^2-provide substrates for endogenous GSH,and then slow down the oxidative damage degree of cells.3.Compared with control,NaCl stress significantly increased the contents of hydrogen peroxide?H₂O₂?,superoxide anion?·O₂^-?and absocrbic acid?AsA?in the leaves of tomato seedlings,and decreased the activities of superoxide dismutase?SOD?,catalase?CAT?,glutathione reductase?GR?,ascorbate peroxidase?APX?,monodehydroascorbate reductase?MDHAR?and dehydroascorbate reductase?DHAR?,as well as the contents of GSH and GSH/GSSG ratio,respectively at 24 h and 72 h after treatments.Compared with the NaCl stress,NaCl+Hb increased the oxidative damage and decreased the NO level,but had no significant effect on GSH contents in the leaves of salt-stressed tomato seedlings.NaCl+GSH significantly increased the contents of GSH and NO and the activities of nitrate reductase?NR?,MDHAR,SOD?except 72 h?,and CAT?except 48 h?during the whole sampling period,as well as the activities of GR,APX and DHAR at 48 and 72 h after treatments,and decreased the electrolyte permeability,the contents of thiobarbituric acid reactive substance?TBARS?and H₂O₂ during the whole sampling period and superoxide anion at 48 and 72 h in leaves of salt-stressed tomato seedlings.The application of GSH also significantly increased the levels of GSH,AsA and NO,the activities of CAT and APX at all three sampling dates,and the activities of NR?except 72 h?and NOS?except 24 h?,and decreased the H₂O₂ and the contents of TBARS and H₂O₂ in leaves of tomato seedlings under NaCl+Hb treatment.These results indicate that exogenous GSH could alleviate the oxidative damage induced by NaCl or NaCl+Hb treatments by up-regulating the levels of GSH and NO,and increasing the activities of antioxidant enzymes and the ROS scavenging capacity.4.Compared with the NaCl treatment,NaCl+GSH significantly increased the activity of NR,the contents of NO and chlorophyll,the stomatal aperture,Fv/Fm and Y?II?values during the whole period.As well as the net photosynthetic rate?Pn?,stomatal conductance?Gs?and transpiration rate?Tr?significantly increased at 48 h and 72 h.While qN and Y?NPQ?showed a gradually decline during the whole treatment.NaCl+Hb treatment significantly increased the contents of proline and soluble sugar,the chlorophyll content and Pn,Gs,Tr value at 48 h after treatment,but it had no significant changes.qN and Y?NPQ?showed a tendency that increased firstly and then decreased during the whole treatment period.NaCl+Hb+GSH treatment significantly increased Pn,Gs,Tr,stomatal aperture,qN and Y?NPQ?at 24 h and72 h during the whole treatment period,and it also significantly reduced the Ls values at 24 h and 72 h after treatment.It showed that the low level of NO was involved in the positive regulation of the photochemical activity and heat dissipation capacity of PSII system after spraying Hb.It can also reduce the chlorophyll degradation by salt stress by increasing the osmotic adjustment substance.Exogenous GSH maintained stomatal opening by mediating the increase of endogenous NO level and osmotic potential.It can also reduce the inhibition of excess light energy on PSII reaction center by increasing the heat dissipation pathway,thereby increasing the photosynthetic rate of plants.Ultimately enhances plant salt resistance.