Effects Of Short-Wave Ultraviolet Radiation On Postharvest Storage Characteristics Of Banana And Its Stress Response Mechanism

Banana（Musa spp.）is a tropical fruit with large yield and high nutritional value.It is a typical respiratory jump fruit,which is easy to deteriorate.UV-C irradiation is a new physical preservation technology with convenient operation,low cost and no residue,but its preservation mechanism is not yet clear.In this paper,the"Brazil"banana（Musa AAA group Brazil）was used as the research object,and UV-C irradiation was used for the preservation of banana.The rules of quality change,carotenoid content,type and total volatile components,antioxidant and softening enzyme activity of bananas during storage were analyzed.At the same time Both transcriptomics and metabolomics were used to explore the differential genes and metabolites of bananas under UV-C stress,and then the reliability of the transcriptomic data was verified by QRT-PCR.Combined with two omics and quality indexes,the mechanism of UV-C banana preservation was comprehensively elaborated.The main contents and results are as follows:（1）Seven different UV-C irradiation doses of 0.008 kJ/m²、0.01 kJ/m²、0.02 kJ/m²、0.03 kJ/m²、0.04 kJ/m²、0.06 kJ/m²、0.08 kJ/m²were compared in banana treatment,and it was found that excessive doses would cause burns or Browning of bananas.If the dose is too small,it has no fresh-keeping effect.According to color and hardness,the optimal dose of banana is 0.02 kJ/m².（2）Treated with UV-C irradiation,the expression of gibberellin（GID1 and Della proteins）,abscisic acid（PYR/PYL and PP2C）and salicylic acid（PR1）signal-related genes were up-regulated,while ethylene responsive transcription factor（ERF057）was down-regulated.The peak of ethylene release was delayed with UV-C irradiation and the peak value(14.96μL/kg·h^-1)was only 69.68%of the CK group(21.47μL/kg·h^-1).The total chlorophyll content in UV-C group was always higher than that in CK group,and the reducing sugar content in CK group was significantly higher than that in UV-C group.Therefore,UV-C irradiation activated genes related to plant hormone signaling pathway,thus inhibiting ethylene release,delaying banana ripening,and maintaining higher chlorophyll content and lower reducing sugar content.（3）The gene expression of zeaxanthin epoxididase increased after UV-C irradiation,affecting the banana carotenoid biosynthesis,and the lutein content increased（from65.63±2.39μg/g in CK group to 81.37±9.24μg/g in UV-C group）.And lutein,which is highly sensitive to ultraviolet light,protects bananas from damage.UV-C irradiation up-regulated phenylpropanoid biosynthesis,flavonoid biosynthesis related genes.Transcriptomic and metabolomics analysis also showed that UV-C induced phenylpropanoid biosynthesis and flavonoid bioanabolism,activated PAL activity,increased TP and TF content,and enhanced the activity of disease resistance-related enzymes（SOD,POD,CAT）;The increased expression of Ca M4,WRKY22,Rboh D,ERECTA and transmembrane protein 222 in MAPK signaling pathway,and the increased expression of cysteine dixygenase synthesized by taurine and subtaurine biosynthesis contributed to maintaining the homeostasis of ROS in banana peel,and significantly reduced the accumulation of superoxide anion radical and H₂O₂in banana.UV-C irradiation activated the expression of pattern recognition receptors（EIX44198 and CERK1）,hypersensitivity related genes（PBS1,HSP90,Htp G）and pathogenicity related genes（PTI5）in plant-pathogen interaction pathway of bananas,induced hypersensitivity and enhanced disease resistance of bananas.Therefore,UV-C irradiation can improve the ability and disease resistance of bananas to remove excess reactive oxygen species,reduce the content of malondialdehyde,improve FRAP,DPPH and ABTS free radical scavenging rate,reduce the spoilage rate,enhance the stress resistance of banana fruit,so as to protect bananas in the storage process.（4）The results of GC-MS showed that esters were the main volatile components in mature banana flesh of CK group and UV-C group.The contents of esters in CK group and UV-C group were 75.98%±0.39%and 76.61%±0.25%,respectively.The esters in the top 10 components of banana in the two groups were the same,and these relatively high esters constituted the characteristic aroma of banana fruits.Iso-amyl acetate and iso-amyl butyrate were the first two volatile components with higher contents,and the contents of these two components increased after UV-C irradiation.Therefore,the total ester content,main characteristic aroma components iso-amyl acetate and iso-amyl butyrate of bananas in UV-C group were slightly higher than those in CK group,and the aroma of bananas irradiated by UV-C did not weaken or even slightly enhanced.Transcriptomic analysis showed that UV-C irradiation affected the lipid metabolism pathway and amino acid metabolism pathway of banana,which may lead to a slight increase in the production of characteristic esters in aroma components.（5）UV-C irradiation upregulated the expression of three alcohol-forming fatty acyl-Co A reductase and an aldehyde detase for kertin,subcutin,and wax biosynthesis and the unsaturated fatty acids（UFA）for fatty acid-hydroxylase biosynthesized in bananas,and increased the amount of wax and UFA content in banana peel.UV-C irradiation up-regulated the expression of 3 PODs,3 trans-cinnamate4-monooxygenase,2 cinnamate co A reductase and 2 PALs in the phenylpropanoid biosynthesis pathway of banana,resulting in increased lignin biosynthesis.Therefore,UV-C irradiation can induce banana peel to produce more wax,UFA and lignin,and reduce the activities of Cx,α-Al and PG,so as to maintain the integrity of banana cell wall,free from disease,maintain fruit firmness,resulting in a longer shelf life and maintain banana quality.