The Effect Of Selenium On DNA Methylation Of Processing Tomato Under Salt Stress And Its Relationship With Salt Resistance

In order to understand the effect of exogenous Se (selenium) on DNA Methylation of Processingtomato under salt stress and its relationship with salt tolerance and provide the theoretical basis forclarifying the biological and molecular mechanism of Se alleviated salt stress and increase salt tolerancein processing tomato. In this study, two contrasting cultivars of tomato (Lycopersicon esculentum Miller)differing in salt tolerance were used as experimental materials to investigate the effects of exogenousselenium (Na2SeO30.05mM）on level of DNA methylation and lipid peroxidation, H2O2content, redoxstate, antioxidant enzymes activity in roots and leaves and related antioxidative enzymes geneexpression in leaves of tomato seedlings under NaCl（100mM）stress. The main results were showed asthe following:1.Comparing with control, the levels of DNA methylation siginificantly increased in roots andleaves of both tomato cultivars under NaCl stress treatment. Both of Se alone treatment and NaCl stresswith Se treatment caused the decrease of DNA methylation level in roots and leaves of both cultivars.Under NaCl stress with Se or without Se treatment, the levels of DNA methylation in roots were higherthan that in leaves of both tomato cultivars. In addition, the saline-tolerance cv. Jiahe No.9had higherDNA methylation levels than saline-sensitive cv. Shuangfeng87-5in roots and leaves of tomatoseedlings.2. Application of Se significantly alleviated salt-induced oxidative stress, especially for thesaline-sensitive cultivar Shuangfeng87-5and dramatically depressed H2O2and malondialdehyde (MDA)accumulation. Se keeped GSH/GSSH， AsA/DHA and NADPH/NADP+ratios over the controlespecially in the case of salt-induced reduce power reduction. External Se counteracted salt-induceddecrease in activities of glutathione peroxidase (GPX) in Grx system and thioredoxin reductase (TrxR)in Trx system and the activities of key enzymes related with the ascorbate-glutathione cycle includingdehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR) and glutathionereductase (GR) in roots and leaves of both cultivars, and decreased the salt-induced increase insuperoxidase dismutase (SOD) after24and72h treatment and ascorbate peroxidase (APX) activities.External Se up-regulated leaf Mn-SOD，POD，MDHAR (except at24h and120h), and GPX and TrxRexpression levele in leaves of both cultivars under normal condition and NaCl treatment. External Sealso up-regulated GR (except at24h) mRNA level in Shuangfeng87-5and DHAR1(except at120h) andGR (except at120h) mRNA level in Jiahe No.9. The gene expression levels of key antioxidativeenzymes in leaves of saline-tolerance cv. Jiahe No.9were higher than that in leaves of saline-sensitivecv. Shuangfeng87-5under NaCl treatment with Se or without Se addition.In conclusion, above results indicated that reduced DNA methylation levels and elevatedintracellular reducing power levels and key antioxidant enzymes activity in Trx, Grx systems andascorbate-glutathione (AsA-GSH) cycle and related antioxidative enzymes gene expression, when concerning ROS (reactive oxygen species) scavenging systems, play an important role in Se increasessalinity tolerance of tomato plants and alleviates salt-induced oxidative stress. In addition, the salttolerance of Jiahe No.9is closely related with higher DNA methylation levels and ROS scavengingcapacity and reducing power levels in root and leaf.