| ’Nanguo’pears are native to Liaoning province. The fruit, normally picked in early September, present unique flavor undergone moderate mature and is deeply appreciated by consumers. However, the harvest time of’Nanguo’pears is centralized, they can just store for half a month, and picked fruit can only be stored for half a month under ambient temperature. After that the fruit becomes ripening and senescence. Low-temperature storage is one of the most effective postharvest technologies to retard senescence and storage period. However, the fruit gradually exhibits pericarp browning during shelf life at room temperature after cold storage, resulting in reduced commodity value. Therefore, it is significant to study the mechanism browning and explore effective method to control browning of the pericarp in ’Nanguo’pears. In this study, changes in the browning substrate and activity of key enzyme, membrane permeability, and the extent of membrane lipid peroxidation were investigated. Changes in the main products, activity and gene expression of enzymes involved in the membrane lipid metabolism pathway were also studied. The objective of this study is to elucidate the role of membrane lipid metabolism in pericarp browning. Futhermore, low temperature condition and intermittent warming treatments were applied to explore regulation on pericarp browning in’Nanguo’pears.1. A cDNA fragment of the PLD gene was isolated from key enzyme involved in the membrane lipid metabolism pathway of ’Nanguo’pears, named PuPLD (GenBank Accession No.KP975510). The cloned partial cDNA sequence of PuPLD was 1336 bp and included a 3’ untranslated regions of 250 bp; the sequence encoded a polypeptide of 361 amino acids. BLAST searches were performed to analyze the homology with PLDs of others species. The sequence alignment result indicated that PuPLD was close to Pyrus pyrifolia and apple. PuPLD was distant to grape, tomato, Arabidopsis, melon, and litchi.2. Pericarp browning gradually appeared when ’Nanguo’pears were kept at room temperature after cold storage for 120 d and 180 d. Moreover, the longer the period of cold storage of’Nanguo’pears, the severer the degree of pericarp browning on the shelf life at room temperature after refrigeration. Significantly higher polyphenol oxidase (PPO) activity and lower total phenolic content were observed in fruit when browning occurred. Fruit kept for 180d in cold storage showed a significant increase in membrane permeability and malondialdehyde (MDA) content as well as significant decrease in linoleic acid content and linolenic acid content compared to fruit stored for 60 d and 120 d. This significant change occurred late in cold storage and was maintained during subsequent shelf life. The activity of lipoxygenase (LOX) was remarkably increased and levels of PuPLD and PuLOX transcripts were markedly up-regulated during cold storage. During shelf life after cold storage, when pericarp browning occurred, the activities of phospholipase D (PLD) and LOX were significantly higher and expressions of PuPLD and PuLOX were significantly increased. These results indicated that the severity of pericarp browning during shelf life is related to the duration of cold storage. Long-term refrigeration resulted in an increase in the activity and expression of PLD and LOX, accelerated the degradation of membrane lipld and the damage of celluar membrane, ultimately leading to the occurrence of browning.3. Low temperature condition and intermittent warming treatments generated pericarp browning in shelf life after cold storage for 120 d, however, the browning index was lower than that in the fruit without pokilothermic treatments. The activity and expression of PLD and LOX were reduced, the degradations of linoleic acid and linolenic acid were inhibited, and the production of MDA was decreased. The increase of PPO activity and decrease of total phenolic content were restrained. Therefore, the pericarp browning of ’Nanguo’pears was allebiated. The effects of low temperature condition treatment was better than that of intermittent warming treatments. |
PDF Full Text Request