Melatonin Alleviates Chilling Injury in Kiwifruit and Its Relationship with Carbohydrate Metabolism
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Abstract:
In order to investigate the relationship between the reduction of chilling injury in kiwifruit by the melatonin (MT) treatment and the carbohydrate metabolism of the fruit, ‘Xuxiang’ kiwifruit was used as the experimental material. The kiwifruits were soaked in the 0.05 mmol/L MT solution and stored at 0~1 ℃ for 90 d. The chilling injury index, firmness, malondialdehyde content and carbohydrate metabolism-related indicators were measured regularly. The results showed that the MT treatment delayed the increase of fruit chilling injury index, the decrease of firmness and the production of malondialdehyde, thus alleviated chilling injury in the kiwifruits. The total amylase activity was found to be inhibited, and during the whole storage, the total amylase activity of the MT-treated fruit was reduced by 41.27% on average compared with that of the control, thereby causing a delayed conversion of starch to soluble sugars, and consequently a higher retained starch content (1.07%) in the kiwifruits. Moreover, the starch content in the MT-treated fruit was significantly negatively correlated with the fruit’s chilling injury index (r=-0.820, p<0.01). The MT treatment decreased the activities of sucrose phosphate synthase, sucrose synthase, acid invertase and neutral invertase, and at the end of the storage, the activities of the four enzymes in the MT-treated fruit were 9.52%, 9.12%, 8.55% and 9.74% lower than those of the control, respectively. Thus, the synthesis-degradation cycle of sucrose was weakened and sucrose accumulation in the fruit slowed down, which induced, to some extent, the delay of starch degradation in the kiwifruit. The comprehensive analysis suggested that starch may be an important biomarker for the occurrence of chilling injury in kiwifruit, and in the effect of MT on kiwifruit may be a result of the co-regulation of total amylase activity and sucrose synthesis-degradation cycle.
