Combined application of HS and a plant growth promoting strain JIL321 regulates photosynthetic efficacy, soil enzyme activity and growth-promotion in rice under salt stress.

Salinity stress is one of the most harmful abiotic stresses that inhibit crop growth and grain yield. In this study, a salt-tolerant bacterium was isolated from the soil of the rice rhizosphere and named Myroides sp. JIL321, based on the results of the phylogenetic tree analysis. The strain JIL321 tolerated up to 1, 283.37 mM of NaCl and exhibited positive plant growth-promoting traits, such as the production of indole acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Therefore, the effects of JIL321 on rice (Oryza sativa L.) under salinity stress were determined. The inoculation of strain JIL321 significantly increased the chlorophyll content and the accumulation of osmotic adjustment substances, such as proline and soluble sugars, in rice expose to salt stress. Additionally, strain JIL321 inoculation significantly enhanced the activities of some enzymes commonly found in soil, such as urease, invertase and catalase. Moreover, the production of hydrogen sulfide (HS), a pivotal signaling molecule, was also induced in rice by salt stress. Treatment with sodium hydrogen sulfide (NaHS, HS donor) improved salt stress tolerance of the rice, while treatment with hypotaurine (HT, HS scavenger) significantly suppressed it. Interestingly, NaHS treatment also improved the production of IAA and ACC deaminase in strain JIL321 under 0 mM and 150 mM salt concentrations. The combined treatment of JIL321 and NaHS could further improve the growth of salt-stressed rice seedlings, most likely due to the interaction effect between HS and strain JIL321. To our knowledge, this study is the first to demonstrate that the combined use of HS and plant growth-promoting bacteria could alleviate the adverse effects of salt stress on rice plants, and further verifies the novel role of HS as a signaling molecule that enhance the tolerance of plant to abiotic stresses.