Exogenous Glutathione Enhances Salt Tolerance in Kenaf by Mediating Modulation of Oxidative Stress Response and DNA Methylation

Kenaf (Hibiscus cannabinus L.) is an important fiber crop, which can be applied for the restoration of saline-alkali land. The objective of our study was to investigate the impacts of exogenous glutathione (GSH) on physiological and biochemical properties, ion balance, and DNA methylation of kenaf under salt stress. We used Hoagland nutrient solution containing 200 mM NaCl to simulate salt stress, and found the growth of kenaf seedlings was substantially hindered. 100 μM GSH pretreatment effectively increased the plant height, stem diameter, main root length, and fresh weight under salt stress, as well as reduced the uptake of Na⁺ and Cl⁻ and promoted the uptake of K⁺. Besides, exogenous GSH pretreatment protected kenaf plants from salt-induced adversities by reducing the ROS-induced oxidative damage, enhancing the contents of chlorophyll, proline, and soluble sugar. Salinity reduced the total DNA methylation level in kenaf genome, triggering higher mRNA expressions of HcGLP3, HcDOF1.4, HcULP3, HcVHA, HcPP2C39, and HcSRF6. However, GSH addition enhanced the total DNA methylation level. We further utilized virus-induced genes silencing technique to confirm that HcGLP3 played a positive role in the response of kenaf to salinity. Taken together, exogenous GSH could enhance salt tolerance in kenaf by mediating modulation of oxidative stress response and DNA methylation.