Effects Of Low Temperature Conditioning And Salicylic Acid Treatment On Chilling Injury Of Peach Fruit And The Possible Mechanicsms

Peach fruit is an important fruit in China, and is very popular for its juicy texture, delicious flavor and rich in nutrient. Peaches are matured in mid-summer, and they are highly susceptible to pathogenic infection and physiological deterioration during ambient temperature storage and ripening. Cold storage is effectively used to control postharvest disease and inhibit ripening of peach fruit. However, chilling injury (CI), such as internal browning and juicelessness, is usually found in peach fruit stored at low temperature for long time. In this paper, the effects of low temperature conditioning (LTC) and salicylic acid (SA) on CI in peach fruit (Prumus persica (L.) Batsch cv. Xiahui5) and the possible mechanisms involved were investigated. The results were as follows:1. Effects of LTC treatments on chilling injuryThe effects of LTC in alleviating chilling injury and the optimum conditions were investigated. Peach fruits were pre-conditioned at temperatures of 4,8 and 12℃for 2,4,6, 8 or 10 days. The results indicated that the control fruit directly stored at 0℃without LTC developed CI symptoms including flesh wooliness and internal browning after 28 days of storage. Fruit LTC at 4℃also exhibited severe CI manifested as flesh leatheriness. Severe internal browning was observed in fruit LTC at 8℃. LTC at 12℃for 6 days was found most effective in inhibiting the development of flesh wooliness and internal browning and maintaining sensory quality. These results suggested that LTC at 12℃for 6 days might be a useful technique to alleviate CI and maintain peach fruit quality during cold storage.2. The possible mechanisms that LTC treatment alleviating chilling injuryLTC at 12℃for 6 days treatment was chosen to investigate the possible mechanisms involved in alleviating CI. The results showed that LTC treatment decreased accumulation of O2·-, H2O2 and MDA contents due to increasing the activities of SOD and CAT significantly, and in addition, the activities of POD and APX and the level of GSH and AsA contents were enhanced, these could keep the balance between the formation and detoxification of active oxygen species. LTC treatment exhibited higher level of respiratory intensity may be attributed to the higher activities of the key enzymes of glucose metabolism. However, little effect was found on CCO activity in LTC treated fruits. It implied that alternative way was probably regulated by respiratory intensity of EMP, TCA, PPP, and LTC treatment enhanced the respiratory intensity of alternative way. The level of polyamines contents were enhanced by LTC treatment significantly, which could alleviate the CI but did not affect ethylene synthesis.3. Effects of SA treatments on chilling injuryPeaches were treated with different concentrations of SA (0.7,1.0 or 1.3 mmol·L-1) to investigate the effects of SA treatments on CI. It was found that fruit treated with 0.7 mmol·L-1 SA developed CI symptoms including flesh wooliness. A decrease in extractable juice was observed in fruit treated with 1.3 mmol·L-1 SA. Treatment with 1.0 mmol·L-1 SA was most effective on maintaining TSS and TA contents, and inhibited the decrease in extractable juice and internal browning. These results suggested that treatment with 1.0 mmol·L-1 SA could be a useful technique to alleviate CI and maintain high peach fruit quality.4. The possible mechanisms that SA treatment alleviating chilling injuryPeaches treated with 1.0 mmol·L-1 SA were chosen to investigate the possible mechanisms involved in alleviating CI. The results showed that SA treatment, similarly to LTC, effectively maintained the activities of SOD, APX, POD and the level of GSH and AsA content, which reduced the accumulation of O2·-, H2O2 and MDA. However, no profound differences in CAT activity were observed in SA treated fruits. SA treatment exhibited lower level of respiratory intensity may be attributed to the lower activities of PGI and MDH, while SA enhanced the activity of CCO significantly. These results indicated that the decrease of the respiratory intensity in SA treatment was mainly due to the alternative way. Peaches treated with SA also showed higher level of polyamines contents but the high polyamines content shown correlated to the inhibition of ethylene synthesis.