| Hami melon?Cucumis melo L.?is one of the important horticultural products in Xinjiang province,which is famous for its crisp,rich flavor and nutrient by the world and liked deeply by consumer.After harvest,the fruit are highly susceptible to pathogenic infection and physiological deterioration during ambient temperature storage.Cold storage can extend the storage period of Hami melon fruit,but it is sensitive to low temperature,and easily cause the occurrence of chilling injury?CI?,and greatly affected the quality and commodity of Hami melon fruit,the technology of cold storage and cold chain logistics applied to production in practice is limited.Thus,it is crucial to study on the characteristic and controlling mechanism of postharvest chilling injury in Hami melon fruit,which is a key obstruction to block the fine development of harm melon industry.In this study,the three local representative Hami melon cultivars?Xizhoumi No.25,Xinmi No.3 and Xinmi No.11?was evaluated,We studied the characteristics of postharvest CI,the difference of cold tolerance and the expression of CBF?C-repeatbinding factor?of three Hami melon cultivars stored at 3±0.5 °C with a relative humidity?RH?of 80 %85 % for 49 d,and explored the controlling mechanism of low temperature conditioning?LTC?and nitric oxide?NO?treatment on CI of Hami melon fruit.It will establish the foundation for the CI evaluation system,and provide some theoretical and technical basis for identification and controlling CI in practice.The results were as follows:1.There were different characteristics of postharvest CI and cold tolerance in three Hami melon cultivars stored at 3±0.5 °C with RH of 80 %85 %.CI symptoms manifested in the rind of ‘Xizhoumi No.25' fruit as brown spots,pitting,skin scald and depression were observed after 21 d of storage at 3±0.5 °C followed by 3 d at 25 °C;Trace CI symptoms were initially found in the rind of ‘Xinmi No.3' fruit after 7 d of storage at 3±0.5 °C followed by 3 d at 25 °C,and a number of fruit showed symptoms,including brown spots,discoloration and rotting.In contrast,only minimal CI symptoms developed in the rind of ‘Xinmi No.11' fruit,due to brown spots and skin scald were visible.CI symptoms in three Hami melon cultivars were mainly found in the peel tissue,but not in the pulp tissue.The CI index and CI incidence of ‘Xinmi No.11' fruit were significantly lower than that of ‘Xizhoumi No.25' and ‘Xinmi 3' during storage at 3±0.5 °C with RH of 80 %85 %,and hardness,TA and Vc content were significantly higher than those two others.After 49 d,The CI incidence of ‘Xinmi No.11' fruit was only 6.67 %,the good fruit rate was as high as 84.44 %,indicating that‘Xizhoumi No.25' and ‘Xinmi No.3' were more sensitive to CI than ‘Xinmi No.11' during storage at 3±0.5 °C with RH of 80 %85 %.2.The incidence of CI in three Hami melon cultivars are related to the active oxygen,membrane fatty acid metabolism and endogenous polyamine metabolisms of the peel tissue during storage at 3±0.5 °C with RH of 80 %85 %.The results of correlation analysis showed that there were positive relationship between linoleic acid?C18:2?,linolenic acid?C18:3?,putrescine?Put?,spermine?Spm?,peroxidase?POD?,superoxide dismutase?SOD?,ascorbate peroxidase?APX?and cold tolerance,and there were negative relationship between ethylene production rate,hydrogen peroxide?H2O2?,malonaldehyde?MDA?,superoxide anion(O2-·),relative membrane permeability,lipoxygenase?LOX?,Palmitic acid?C16:0?and cold tolerance of postharvest Hami melon fuit,suggesting that the mentioned-aboved ind indexes in the peel tissue could be used as the key evaluation indicators of cold tolerance of Hami melon fruit,and also could predict the indicators of the incidence of CI in Hami melon fruit.3.Cm CBF1?Gen Bank accession number: KT737742?and Cm CBF3?Gen Bank accession number: KT737743?were isolated and cloned from Hami melon fruit,and encoded 212 amino acids and 204 amino acids,respectively.Sequence analysis showed that Cm CBF1 and Cm CBF3 contained a highly conserved AP2 / EREBP DNA binding domain and AP2/ERF containing highly conserved CBF signal sequences and other characteristic domains.The phylogenetic tree analysis showed that Cm CBF1 was close to Md CBF1,and Cm CBF3 was close to Cs CBF3.The relative expression of Cm CBF1 and Cm CBF3 were induced by RT-q PCR,Cm CBF1 and Cm CBF3 genes showed specific expression in the peel and pulp tissues of different Hami melon cultivars,the expression of Cm CBF1 and Cm CBF3 in the peel and pulp tissues were short-term expression at 6 h and 12 h,respectively.The peak expression was observed at 14 d and 21 d,and Cm CBF3 was induced more strongly under storage at 3±0.5 °C with RH of 80 %85 %.The relative expression of Cm CBF1 and Cm CBF3 in the peel and pulp tissues of ‘Xinmi No.11' were significantly higher than those of ‘Xizhoumi No.25' and ‘Xinmi No.3',indicating that the expression of Cm CBF1 and Cm CBF3 were positively correlated with cold tolerance of Hami melon fruit.4.The CI index,the incidence of CI,the weight loss rate,the good fruit rate and quality characters?fmness,SSC,TA and Vc?of ‘Xizhoumi No.25' fruit were evaluated under different LTC treatments?3,6,9 d at 10 °C before cold storage at 3±0.5 °C with RH of 80 %85 %?on CI.The results showed that LTC treatment?3 d at 10 °C before cold storage at 3±0.5 °C?alleviated CI via inhibiting the respiration rate and ethylene production,improved the activities of SOD,POD,CAT and APX,decreased O2-·and H2O2,and reduced the relative membrane permeability and MDA contents.Simultaneously,LTC induced the expression of Cm CBF1 and Cm CBF3,and maintained abscisic acid?ABA?,indo1e-3-acetic acid?IAA?and gibberellin acid?GA?at a high level,inhibited the activities of LOX and polyphenol oxidase?PPO?,reduced the water evaporation of the peel tissue,and alleviated the symptoms of CI,including brown spots,pitting,skin scald and depression of ‘Xizhoumi No.25' fruit under 3±0.5 °C.After 49 d,the weight loss rate was only 6.85 %,and the good fruit rate was 40.67 %,and kept a high fruit hardness,soluble solids and vitamin C content.5.‘Xinmi No.11' fruit were pre-treated with 0?20?60 and 100?L/L NO for 3 h at 25 ?,and then stored at 1±0.5 ? with a relative humidity?RH?of 80 %85 %.for 49 d.The CI index,the incidence of CI,the weight loss rate,the good fruit rate and quality characters?fmness,SSC,TA and Vc?of fruit were evaluated.The results showed that 60 ?L/LNO treatment alleviated and delayed CI for 7 d,the incidence of CI was 26.67% lower than that of the control samples.One hand,NO treatment kept the higher Put,Spm and spermidine?Spd?content which inhibited the production of ethylene and delayed the peak time of ethylene,and alleviated and delayed the occurrence of CI;On the other hand,NO treatment could significantly increase the activities of SOD,POD,CAT and APX in the peel,accelerated proline,soluble protein and soluble sugar content,maintained the lower O2-·and H2O2 content in the peel tissue,and reduced the damage of the reactive oxygen species to the cell membrane and improved the integrity of the cell membrane.In addition,NO treatment could also enhance the cold tolerance via inducing the expression of Cm CBF1 and Cm CBF3 in the peel tissue of Hami melon fruit during storage at 1±0.5 ?.Thus,to maintaining the firmness,SSC,Vc content and good fruit rate of Hami melon fruit during shelf-life. |
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