The Signal Mechanism Of Hydrogen Sulfide Alleviating Postharvest Ripening And Senescence Of Apples

Hydrogen sulfide (H2S), similar to carbon monoxide (CO) and nitric oxide (NO), has been identified as the third multifunctional signaling molecule in plants. Recent research indicates that H2S functions in various physiological processes in plants, including seed germination, root organogenesis, abiotic stress tolerance, photosynthesis, guard cell movement, and postharvest senescence. Our previous research has been shown that H2S could alleviate the process of ripening and senescence in respiratory climacteric of kiwifruits, non-respiratory climacteric of strawberry. However, the effect of H2S on delaying ripening and senescence of fresh-cut apple remains unknown. In the present study, the effect of H2S on postharvest shelf life, antioxidative metabolism, and senescence-related gene expression of apple was investigated. Our results showed that H2S donor NaHS solutions significantly delayed ripening and senescence of fresh-cut apples in a dose-dependent manner with the optimal concentration of 0.4 mM NaHS solution. Further investigations showed that H2S delayed the rot index and browning degree, inhibited respiration rate and maintained higher levels of metabolites, such as starch, reducing sugar, soluble protein and total soluble solid (TSS), at the same time, H2S fumigated apple slices contained lower levels of free amino acids compared with controls, and thus improved the performance of fresh-cut apple during storage.It is generally accepted that overproduction of reactive oxygen species (ROS) is involved in ripening and senescence of fruit and vegetable. The effect of H2S on antioxidant metabolism in postharvest apples was investigated. The results showed that H2S treatment significantly reduced the accumulation of hydrogen peroxide (H2O2), superoxide anion (·O2-) and malondialdehyde (MDA), maintained significantly higher activities of ROS-scavenging system, such as antioxidant enzyme including ascorbate peroxidase (APX), catalase (CAT), dehydroascorbate reductase (DHAR), glutathione reductase (GR), guaiacol peroxidase (POD) and superoxide dismutase (SOD) and other natural antioxidants such as ascorbic acid, total phenolics, and flavonoids, while lower activities of lipoxygenase (LOX), phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), polygalacturonase (PG) and protease were observed compared with untreated controls. We interpret these data as indicating that H2S functions as an antioxidant to extend the postharvest life of fresh-cut apples during storage.Moreover, we also investigated the effects of H2S in antioxidant metabolism, ethylene biosynthesis and signal transduction, fruit softening and disease resistance-related gene expression, and showed that exogenous H2S could significantly up-regulated the expression of MdAPX, MdCAT, MdDHAR, MdSOD, MdGR, and MdCHI, Md?-1,3-G, MdNBS-LRRl and MdPR1,2,5,10, MdICS2, and down-regulated the expression of MdLOX2, MdPAL, MdCP, MdPPO, MdACO1, MdERSl, MdETRl and MdPGl, MdPME, Mda-L-Af and Md?-Gal in postharvest apple tissue.In conclusion, the present study indicates that H2S treatment not only helps to eliminate ROS overproduction, improve the antioxidant capacity, but also affects the expression of senescence-related genes in apples, suggesting that H2S has the potential to maintain higher fruit quality and delay postharvest senescence of fresh-cut apples.