Isolation and Assaying of polysaccharides in Portulaca oleracea Effect of Exogenous Hydrogen Sulfide on Photosynthesis and Antioxidant System of Cucumber Leaves Under Low Temperature in Solar-Greenhouse Effect of Exogenous Hydrogen Sulfide on Photosynthesis and Antioxidant System of Cucumber Leaves Under Low Temperature in Solar-Greenhouse H2S acts downstream of H2O2 in the regulation of grapevine Resistance to Plasmopara viticola Relationship between H2S Signal and WRKY in ABA Regulating Root Growth and Stomatal Movement