Abstract
BackgroundBagging is one of the most important techniques for producting high-quality fruits. In the actual of cultivating, we found a new kind of browning in peel of apple fruit that occurs before harvest and worsen during storage period. There are many studies on metabonomic analysis of browning about storage fruits, but few studies on the mechanism of browning before harvest.ResultsIn this study, five-year-old trees of ‘Rui Xue’ (CNA20151469.1) were used as materials. Bagging fruits without browning (BFW) and bagging fruits with browning (BFB) were set as the experimental groups, non-bagging fruits (NBF) were set as control. After partial least squares discriminant analysis (PLS-DA), 50 kinds of metabolites were important with predictive VIP > 1 and p-value < 0.05. The most important differential metabolites include flavonoids and lipids molecules, 11 flavonoids and 6 lipids molecules were significantly decreased in the BFW compared with NBF. After browning, 11 flavonoids and 7 lipids were further decreased in BFB compared with BFW. Meanwhile, the significantly enriched metabolic pathways include galactose metabolism, ABC membrane transporter protein, flavonoid biosynthesis and linoleic acid metabolism pathways et al. Physiological indicators show that, compared with NBF, the content of malondialdehyde (MDA), hydrogen peroxide (H2O2), superoxide anion (O2−) in peel of BFW and BFB were significantly increased, and the difference of BFB was more significant. Meanwhile, the antioxidant enzyme activities of BFW and BFB were inhibited, which accelerated the destruction of cell structure. In addition, the metabolome and physiological data showed that the significantly decrease of flavonoid was positively correlated with peel browning. So, we analyzed the expression of flavonoid related genes and found that, compared with NBF, the flavonoid synthesis genes MdLAR and MdANR were significantly up-regulated in BFW and BFB, but, the downstream flavonoids-related polymeric genes MdLAC7 and MdLAC14 were also significantly expressed.ConclusionsOur findings demonstrated that the microenvironment of fruit was changed by bagging, the destruction of cell structure, the decrease of flavonoids and the increase of triterpenoids were the main reasons for the browning of peel.
Highlights
Bagging is one of the most important techniques for producting high-quality fruits
The epithelial cells of the nonbagging fruits (NBF) included 5–6 layers (Fig. 3a), while the upper epidermal cells of the bagging fruit (BFW and bagging fruits with browning (BFB)) had only 4–5 layers (Fig. 3b-c), indicating that bagging changed the microenvironment around the fruit and reduced the number of cell layers in the peel
This conclusion is consistent with the results we have measured (Fig. 8), after bagging, more Hydrogen peroxide (H2O2), O2− and MDA were produced in the peel, which accelerated the destruction of cell structure
Summary
Bagging is one of the most important techniques for producting high-quality fruits. In the actual of cultivating, we found a new kind of browning in peel of apple fruit that occurs before harvest and worsen during storage period. Fruit bagging as one of the most important good agricultural practice to produce high quality fruit [2, 3] It has been used in several fruit crops to improve the peel color and surface smoothness, and to reduce the incidence of disease, insect pests, sunburn of the peel, and bird damage [3,4,5,6,7,8]. It has been widely used in China, Australia, Japan, and the United States for the cultivation of peach, apple, pear, grape, loquat and so on [3, 9]. The dark condition could inhibit the synthesis and accumulation of antioxidant substances, such as flavonoids and phenols in fruits [11,12,13], thereby reduced the fruits’ resistance to stress
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