Hydrogen sulfide inhibits tomato fruit ripening by restraining fruit softening and ethylene production

Hydrogen sulfide (H2S) plays various roles in plant growth, development and stress response. However, the mechanism of action of H2S in fruit ripening remains unclear. This study investigated the roles and mechanisms of H2S in tomato (Solanum lycopersicum) fruit repining. The results showed that compared with the control (distilled water), H2S treatment significantly delayed the color and hardness transition of tomato fruit; while an H2S scavenger hypotaurine (HT) treatment promoted the color and hardness transition. H2S increased the endogenous chlorophyll content, activity of chlorophyll synthesis-related enzymes, and expression of chlorophyll synthesis-related genes and decreased the expression of chlorophyll degradation-related genes and lycopene content. In contrast, HT decreased the activity of chlorophyll synthesis-related enzymes and expression of related genes; and increased the expression of chlorophyll degradation-related genes. In addition, the activity of the softening-related enzymes, ACS and ACO, ethylene content, and the expression of softening- and ethylene biosynthesis-related genes were decreased by H2S but increased by HT. Exogenous H2S increases endogenous H2S levels. Therefore, H2S may delay tomato fruit ripening by down-regulating the expression of softening-related and ethylene synthesis-related genes and reducing the activity of softening-related and ethylene synthesis-related enzymes.