NO, hydrogen sulfide does not come first during tomato response to high salinity.

High salinity greatly impacts agriculture, particularly in tomato (Solanum lycopersicum), a crop that is a model to study this abiotic stress. This work investigated whether hydrogen sulfide (H2S) acts upstream or downstream of nitric oxide (NO) in the signaling cascade during tomato response to salt stress. An NO-donor incremented H2S levels by 12-18.9% while an H2S-donor yielded 10% more NO in roots. The NO accumulated in roots one-hour after NaCl treatment while H2S accumulation started two-hour later. The NO stimulated H2S accumulation in roots/leaves, but not the opposite (i.e H2S was unable to stimulate NO accumulation) two-hour post NaCl treatment. Also, NO accumulation was accompanied by an increment of transcript levels of genes that encode for H2S-synthesizing enzymes. Our results indicate that H2S acts downstream of NO in the mitigation of oxidative stress, which helps tomato plants to tolerate high salinity.