Physiological Metabolisms Of Inhibition Of Softening Of Postharvest Peach Fruit By NO And H₂S

Hydrogen sulfide (H2S) is considered to be the third gaseous transmitter after nitricoxide (NO) and carbon monoxide (CO). H2S can be synthesized in mammal and involvedin a variety of life activities and processes including the regulation of vascular relaxation,nerve conduction. More and more studies showed that plant can synthesize endogenousH2S, and it has proven to be involved in the regulation of stomatal closure, seedgermination, root development, drought-resistant, heavy metal stress and variety ofphysiological processes in plant. NO has been shown as an endogenous gaseous signalingmolecule involved in regulating a variety of postharvest fruits and vegetables ripening andsenescence. Given the similarity of H2S and NO, H2S may regulate of ripening andsenescence in fruits and vegetables. However, the mechanism of aging process mediatedby H2S in plants is unclear. In our research, the effects of NO, H2S and NO-H2S onpreservation, active oxygen metabolism, ethylene synthesis metabolism and cell wallmetabolism in pesch fruit were studied to explore tne regulation metabolism of NO andH2S on the softening in postharvest peach fruits.Experiments were conducted to study the effects of hydrogen sulfide on the qualitiesand metabolism of reactive oxygen of postharvest ‘Shahong’ peaches. The fruits weredipped in various concentrations of hydrogen sulfide (H2S,15,30,45μmol L-1)respectively and stored at low temperature (0±0.5℃). The rot index, weight loss, solublesugar content (SSC), firmness, ethylene production were determined to evaluate the effectsof H2S treatment on the postharvest life of peaches. Superoxide free radicals (O-2·)production, H2O2content, relative leakage rate, activities of superoxide dismutase (SOD),catalase (CAT) and peroxidase (POD) in peaches were investigated to discuss the role ofH2S on regulating the antioxidant system of peaches. The results showed that, comparedwith control, treatment with15μmol L-1H2S significantly inhibited the increase of rotindex, weight loss, soluble sugar content and the decrease of firmness, and inhibitedethylene production. Treatment with15μmol L-1H2S significantly inhibited superoxidefree radicals (O2·-) production, H2O2content and the increase of relative leakage rate,delayed the decrease of SOD and CAT activity. Treatments with30and45μmol L-1H2Spromoted the ripening and senescence of peaches. Exogenous H2S of low concentration(15μmol L-1) treatment could delay the maturation and senescence of peaches byinhibiting the ethylene production, improving protective enzyme activities and decreasingthe accumulation of reactive oxygen species to protect cell membrane during storage,while high concentration (30,45μmol L-1) proved to be harmful.Experiments were conducted to study the effects of15μl L-1NO,20μl L-1H2S and15μl L-1NO-20μl L-1H2S on the qualities of postharvest ‘Dahong’ peaches storaged at5℃ and25℃, and the effects of ethylene synthesis metabolism in peaches storaged at25℃.The results showed that, compared with control, treatment with NO, H2S and NO-H2Sinhibited the increase of soluble sugar content and the decrease of the titratable acidecontent and firmness to extend the shelf life of Peach Fruit. Compared with the control,NO, H2S, NO-H2S treatment significantly inhibited the activities of ACS and ACO, buttheir effects were different for the accumulation of ACC and MACC. H2S promotedconversion from ACC to MACC to reduce the accumulation of ACC; NO-H2S inhibitedthe contents of ACC and MACC as well. Our treatments reduced the release of ethylenepeach fruit during storage. The results show that, NO, H2S, NO-H2S could delay thematuration and senescence of peaches by inhibiting the ethylene production.Experiments were conducted to study the effects of15μl L-1NO,20μl L-1H2S and15μl L-1NO-20μl L-1H2S on the redistribution of cell wall components to delay the changein the texture of postharvest ‘Dahong’ peaches storaged at5℃and25℃. The result showsthat NO, H2S, NO-H2S significantly inhibited the increase of water and CDTA-soluble cellwall residents in peach fruit during storage, delaying the decrease of Na2CO3,1mol L-1KOH and4mol L-1KOH soluble residents. NO, H2S, NO-H2S inhibited PE, Exo-PG,EGase activity and promoted Endo-PG activity, inhibited the expression of PE, PG, EGaseduring storage, and maintained the texture. NO, H2S, NO-H2S regulated the balance ofbetween PE and PG and inhibited EGase activity, then alleviated chilling injury.