Polyamine accumulation and responses of mango fruit to postharvest polyamine application

Abstract

Mango (Mangifera indicia L.) is a popular tropical fruit which has a great value in both domestic and international markets. Mango is a climacteric fruit which ethylene production increases dramatically, thus leading to a quick ripening process and a short postharvest life. Polyamines (PAs) have been reported to be involved in fruit ripening. Changes in endogenous free polyamines accumulation were measured in two mango cultivars; ‘Nam Dok Mai No.4’ and ‘Nam Dok Mai Si Tong’. Mangoes were allowed to ripen at 25±1 ºC after harvest. It was found that ‘Nam Dok Mai No.4’ mango exhibited higher ethylene production, respiration rate, soluble solid contents and lower titratable acidity than ‘Nam Dok Mai Si Tong’ mango. During fruit ripening, Putrescine (PUT) content decreased and displayed no significant differences between both cultivars. SPD and SPM contents constitutionally increased and were higher in ‘Nam Dok Mai Si Tong’ mango than ‘Nam Dok Mai No.4’ mango. In addition, ‘Nam Dok Mai No.4’ mango, which had a higher ethylene production and a lower level of PAs showed greater market qualities than ‘Nam Dok Mai Si Tong’, which displayed a lower ethylene production. These results suggested that polyamines, especially spermidine (SPD) played a rejuvenating role and regulated mango fruit ripening. The increase in PAs contents may be related to a delay of mango ripening through the reduction of ethylene production. Application of polyamines after harvest also represents a safe and potentially effective method for improving quality and maintaining shelf life of mango fruit. ‘Nam Dok Mai NO.4’ mango was immerged in 0, 1, 2 and 4 mmol/L PUT for 20 minutes and stored at 14 ℃ for 9 days, then transferred to 25 ℃ for another 9 days. The physiological and chemical changes of treated fruit were measured on days 0, 9, 12, 15, and 18. The results showed the most effective treatment was 2 mmol/L PUT, which significantly reduced ethylene production, respiration rate, weight loss, total soluble solids, and increased titratable acidity. In addition, 2 mmol/L PUT treatment increased fruit firmness, reduced soluble pectin content, polygacturonase and pectin methyl esterase activities during storage period. Moreover, our results revealed that the exogenous application of 2 mmol/L PUT increased superoxide dismutase, catalase, guaiacol peroxidase, ascorbate peroxidase and glutathione reductase activities and total antioxidant activities by DPPH radical scavenging and FRAP during storage. The reduction of ethylene production was correlated with the increase of endogenous PAs after exogenous application of PUT. These findings suggested that postharvest exogenous application of 2 mmol/L PUT can be used as an effective method for prolonging storage life and maintaining the quality of ‘Nam Dok Mai No.4’ mango after harvest.