Effects Of Exogenous Melatonin And Heat Treatment On Chilling Injury Of Peach

peach is sensitive to low temperature.low temperature can cause cold damage(CI)and shorten the storage period of juicy peach.In order to alleviate the peach fruit CI and extend the storage period,fresh peach fruit were used as the material,exogenous melatonin and heat treatment were applied to preserve the peach freshness,through storage quality,active oxygen metabolism,energy metabolism,metabolomics and transcription sequencing analysis to explore the impact of two fresh-keeping methods on the occurrence of juicy peach CI.the main findings are as follows:(1)Screening of the optimal concentration of exogenous melatoninDifferent concentrations of exogenous melatonin all can maintain the good quality of peach,but the effect of preservation is different.sensory evaluation found that 100 ?mol/L melatonin treated peach fruit had the best storage quality.Physiological index measurements found that 100?mol/L melatonin treatment of peach fruit significantly inhibited the increase in weight loss rate,relative conductivity and malondialdehyde(MDA)content of peach,slowing down hardness,soluble solids(TSS),protein and brightness(L*)decline,so 100?mol/L melatonin was used to treat peach fruit for further research.(2)The effect of melatonin treatment on the transcriptome and metabolites change of peach fruit under chilling stressThere were 508 differentially expressed genes in control group and melatonin-treated peach fruit,244 differentially expressed genes were up-regulated,264 differentially expressed genes were down-regulated,and 322 differentially expressed genes were annotated to GO database.the 193 differentially expressed genes in the control and melatonin treatment samples were annotated to 26 functions in the COG database,most of the differentially expressed genes mainly involved the following functions,followed by general function prediction only,carbohydrate transport and metabolism,transcription,signal transduction mechanism,post-translational modification,protein conversion,chaperone protein,cell wall/membrane/envelop biogenesis and other six processes.the annotation results of peach in the control group and melatonin treatment group in the KEGG database showed that 103 differentially expressed genes were related to metabolism,31 differentially expressed genes were related to genetic information processing,8 differentially expressed genes were related to environmental information processing,7 related to biological systems,the five differentially expressed genes were related to cell process metabolism.through GC-MS,a total of 28 substances were identified,these included 4 kinds of amino acids,7 kinds of organic acids,6 kinds of sugars and 11 kinds of polyamines.(3)Effects of exogenous melatonin and heat treatment on active oxygen metabolism in the process of peach fruit cold injuryCompared with the control group,exogenous melatonin treatment can suppress the increase of MDA content and relative conductivity of peach fruit.heat treatment can also reduce the symptoms of peach CI,but the treatment effect is not as good as the melatonin treatment group.exogenous melatonin combined with heat treatment can effectively inhibit the increase of CI index,decay rate,weight loss rate and malondialdehyde(MDA)content of peach during cold storage,and improve the superoxide dismutase(SOD)of peach fruit during storage.catalase(CAT),ascorbate peroxidase(APX),dehydroascorbate reductase(DHAR),single dehydroascorbate reductase(MDHAR)activity,enhance the antioxidant capacity of peach during storage,to maintain the storage quality of peach.(4)Effects of exogenous melatonin and heat treatment on energy metabolism in the process of peach fruit cold injuryCompared with the control group,the heat treatment,melatonin treatment alone and combined treatment all inhibited the decrease of the content of adenosine triphosphate(ATP)and adenosine diphosphate(ADP)in post-harvest peach,which kept the energy charge at high level,in which the combined effect is the best.both heat treatment and melatonin treatment can suppress the decline of the vital enzymes succinate dehydrogenase(SDH)and cytochrome oxidase(CCO)in the tricarboxylic acid cycle,and maintain the normal function of mitochondria,the combination works best.The combination of melatonin and heat treatment can effectively inhibit the decline in the activity of H+-ATPase,Ca2+-ATPase,phosphofructokinase(PFK),NADK enzyme,and alternating oxidase(AOX)in peach,and maintain low levels of nicotinamide adenine dinucleotide(NAD)and reduced nicotinamide adenine dinucleotide (NADH) content.