Hydrogen sulfide enhances alfalfa (Medicago sativa) tolerance against salinity during seed germination by nitric oxide pathway

The molecular mechanisms and signal transduction pathways of hydrogen sulfide (H2S) in plant biology are still unclear. Here, by using pharmacological and biochemical approaches, we report that H2S promotes germination and alleviates salinity damage involving nitric oxide (NO) pathway. Upon 100 mM NaCl treatment, both H2S donor sodium hydrosulfide (NaHS) and NO donor sodium nitroprusside (SNP) at 100 mu M could significantly attenuate the inhibition of alfalfa (Medicago sativa) seed germination and thereafter seedling growth inhibition. Meanwhile, the ratio of potassium (K) to sodium (Na) in the root parts was increased. Total, isozymatic activities or corresponding transcripts of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD), or ascorbate peroxidase (APX) were activated differentially, thus resulting in the alleviation of oxidative damage. The above protective roles of NaHS might be related to the induction of endogenous NO, because the addition of the specific scavenger of NO 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO) reversed above effects. Meanwhile, NaHS-triggered NO production was confirmed. Our observations indicate that H2S enhances plant responses against salinity stress by reducing oxidative damage, which might have a possible interaction with NO.