Study On The Mechanism Of H₂S Regulating Healing And Cold Tolerance Of Grafted Tomato Seedlings

Tomato(Solanum lycopersicum L.)is the vegetable crop with the largest area under facility cultivation in China.In actual production,it often encounters problems such as succession barriers,soil-borne diseases and low-temperature stress,which cause a decrease in its quality and yield.Grafting is currently one of the most effective methods to control major diseases and improve plant resistance.However,tomato grafted seedling culture also suffers from long cultivation period and vulnerability to low temperature stress.It has been shown that the gas signaling molecule hydrogen sulfide(H2S)has an important role in the regulation of plant growth and development and abiotic stresses.However,the regulatory mechanism of H2 S on the healing of grafted rootstock and cold tolerance of grafted seedlings is not clear.Therefore(1)The effect of H2 S on regenerated root systems of tomato rootstocks was investigated using broken rootstocks without added sodium sulfide hydrogenation(Na HS,the donor of H2S)as control and broken rootstocks with Na HS added in the nutrient solution as treatment.(2)Grafted seedlings without Na HS added as control and grafted seedlings with Na HS added in the nutrient solution as treatment to investigate the effect of H2 S on graft healing.(3)The physiological mechanisms of H2 S and jasmonic acid(JA)regulation of low temperature stress in tomato grafted seedlings were investigated in depth using normothermic H2 O treatment as control and exogenous sprays of Na HS,methyl jasmonate(Me JA),hyturine(HT,H2 S scavenger)and sodium diethyldithiocarbamate(DIECA,jasmonic acid biosynthesis inhibitor)as treatments.1、0.2 mmol·L-1 Na HS treatment significantly increased root vigor,root length,root number,root area,root volume,and plant biomass in tomato rootstock with broken roots compared with the control;0.1 and 0.3 mmol·L-1 Na HS were not significantly different compared with the control;higher concentrations(0.5 mmol·L-1)of Na HS treatment significantly inhibited regenerative root growth,The 0.2 mmol·L-1Na HS+0.2 mmol·L-1 hypotaurine(HT,H2 S scavenger)treatment partially eliminated the promotion of root vigor by exogenous H2 S,and 0.2 mmol·L-1HT inhibited the level of root vigor.It showed that H2 S could promote the growth and development of tomato rootstock with broken roots and exhibited a low-promoting and high-suppressing effect.2、The exogenous Na HS treatment promoted the healing process of tomato grafted seedlings by analyzing the histology,carboxy fluorescein diacetate(CFDA)staining observation and magenta uptake during the healing process of tomato grafted seedlings.Further studies showed that exogenous Na HS accelerated growth hormone and jasmonic acid production by increasing antioxidant enzyme activity,phenylalanine aminolase(PAL)and polyphenol oxidase(PPO)activity in leaves and rootstock junctions,decreasing reactive oxygen species(ROS)content,and inducing the expression of Sl IAA3,Sl IAA4,Sl PIN4,Sl LOXB,and Sl LOXD,thus promoting formation of healing tissues and vascular bundle bridges,and promote the healing process.3、Under low temperature stress,H2 S significantly induced endogenous JA production in tomato grafted seedling leaves,while Me JA treatment had no significant effect on changes in endogenous H2 S content in leaves.the accumulation of electrolyte leakage(EL),malondialdehyde(MDA),hydrogen peroxide(H2O2)and superoxide anion radicals(O2.-)was significantly reduced in Na HS and Me JA treated tomato grafted seedlings.Superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),reduced/oxidized glutathione(GSH/GSSG),reduced/oxidized ascorbic acid(As A/DHA)and photosynthesis were significantly higher.It is suggested that H2 S and JA can mitigate the damage caused by low temperature stress to tomato grafted seedlings and enhance their cold tolerance by regulating photosynthesis,antioxidant enzyme activity and the redox status of glutathione and ascorbic acid in tomato grafted seedlings.DIECA attenuated the promotion of cold tolerance in tomato grafted seedlings by Na HS,while HT had little effect on JA.This suggests that H2 S may be located upstream of JA in the regulation of cold tolerance in tomato grafted seedlings.