Study On The Regulation Mechanism Of Near-freezing Temperature Storage On Storage Quality And Softening Of Xinjiang Prunus Domestica L.Ximei

’France’ prune(Prunus domestica L.cv.Ximei)fruit is sweet and sour,rich in nutrition,and deeply loved by consumers.However,fresh ’France’ prune has high sugar content and soft tissue,and is susceptible to mechanical damage and microbial disease after harvest,which leads to the acceleration of fruit ripening and softening,and seriously affects its transportation and marketing.Therefore,it is urgent to find a way to delay the ripening and softening of ’France’ prune.’France’ prune fruit is not suitable for storage,while near-freezing temperature(NFT)storage can maintain the nutritional value of the fruit without damaging the cell tissue,and can prolong the storage period by inhibiting the ethylene,respiratory metabolism and enzyme activity in the organism of the fruit.Therefore,in this study,the effects of different storage temperatures(25±0.5℃,4±0.5℃、-1.5℃～-1℃)on physiological quality,active oxygen metabolism and cell wall metabolism of ’France’ prune fruit were compared,and the transcriptome sequencing technology was combined to analyze the changes in the transcription level of ’France’ prune fruit,so as to delay the softening of ’France’ prune fruit by temperature control.It provides some theoretical guidance for extending the storage life and industry development of ’France’ prune fruit.The results are as follows:1.The supercooling point of ’France’prune is-3℃ and the freezing point is-2.1℃.To avoid freezing damage,the NFT storage temperature of ’France’ prune was set to-1.5℃～-1℃.Compared with 25±0.5 ℃ and 4±0.5 ℃,NFT could prolong the storage period of‘France’prune to 49 d,delay the water loss of fruit,inhibit the accumulation of malondialdehyde and the increase of hydrogen peroxide and superoxide anion production rate,reduce and delay the respiration(23.90%)and ethylene peak(11.71%)of fruit.At the end of storage,NFT maintained high fruit firmness(0.35±0.02 N),ascorbic acid(4.13 mg 100 g-1)and total phenol(14.12 mg g-1)contents.In addition,NFT maintained high levels of antioxidant enzyme activity.2.NFT effectively delayed the ripening and softening process of ’France’ prune fruit by inhibiting the expression of cell wall degradation-related genes(ADPG2,PME31,Cx6,BGAL3,α-ARF and EXPA1)and the activities of cell wall-degrading enzymes(PG,PME,Cx,β-GAL and α-ARF),and then maintaining high contents of chelated soluble pectin(1.62 g kg-1),Na2CO3-soluble pectin(3.27 g kg-1),cellulose(3.07 g kg-1)and hemicellulose(10.62 g kg-1)at the end of storage.In addition,NFT delayed the production of water-soluble pectin and lignin and maintained high xyloglucan endotransglucosylases activity.Ultramicroscopic observation showed that the cell wall and double membrane structure of fruit stored at NFT remained intact and tightly connected.3.Since most of the cell wall metabolism-related indicators of ’France’ prune showed significant transitions at day 30 of storage,it was hypothesized that this might be a critical time point for ’France’ prune softening,so ’France’ prune samples for day 0 and day 30 of storage were selected for transcriptome sequencing.The results showed that a total of 4984 differentially expressed genes(DEGs)were identified in the LT30 vs NFT30 comparison group.These DEGs were significantly enriched in plant hormone signal transduction,biosynthesis of secondary metabolites,galactose metabolism,pentose-glucuronate interconversions pathways.In addition,NFT may regulate the ripening and softening process of ’France’ prunes by inducing the expression of cell wall metabolism(ADPG2,PME31,EXPA3 and GAUT13),plant hormone signal transduction(SAMS1,ACS1,ERF106,JAR6 and IAA26),secondary metabolites biosynthesis(PAL1,PER45,CYP75B2 and UGT78G1),and TFs(NAC089,ERF026 and NAC083)related genes.In conclusion,NFT is suitable for storage and fresh-keeping of ’France’ prune fruit.It can delay the degradation of cell wall polysaccharides by regulating the expression of related genes and key metabolic pathways,protect the integrity of cell wall structure,delay the softening of fruit,and maintain high sensory quality and antioxidant activity of fruit.