Metabolomic insights into the browning of the peel of bagging ‘Rui Xue’ apple fruit

Abstract

Background 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. There are many studies on metabonomic analysis of browning about storage fruits, but few studies on the mechanism of browning before harvest. Results In 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. Conclusions Our 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.

Physiological Characteristics of Sunburn Peel after Apple Debagged

“…Sunburn in fruits triggers the production of ROS, and their over-production leads to cell membrane peroxidation, extravasation of intracellular fluid, and an imbalance in metabolism. The over-production of O 2 − (the intermediate product of membrane lipid peroxidation) leads to oxidation in cells and causes degradation of lipids, which increases the MDA content in cells [3,[25][26][27]. In our study, the O 2 − content of BFN and BFA showed no significant differences, which indicates that at the beginning of sunburn injury, the higher scavenging effect in the pericarp cells overcomes the increasing concentrations of ROS [28].…”

“…The biochemical characteristics of different antioxidant enzymes make them have different inducibility in gene expression levels, which enables the antioxidant system to scavenge excessive ROS [6]. CAT, POD, PPO, SOD, and APX are the main antioxidant enzymes for scavenging reactive oxygen species (ROS) [3,33]. SOD is the first line of defense against oxidation in plants.…”

“…is one of the major fruits growing throughout the world [1]. Bagging of the apple fruits is a major cultivation measure to effectively improve the quality of apple by having a clean fruit surface, better color, and no or minimum pesticide residue [2,3]. However, fruits that have been bagged for a long time are very sensitive to sunlight, and the direct solar radiation or reflected light often leads to photooxidative sunburn, and its extended exposure results in sunburn [4].…”

“…Due to the high altitude and dry climate, sunburn is a major factor affecting the development of the local apple industry, which is relatively common. Several studies have determined the role of fruit bagging in improving apple fruit quality and yield [3,5]; however, the debagging of fruits prior to harvesting leaves them prone to sunburn, and the differences in physiological index changes between debagged and non-bagged apple fruits remain to be further studied. Very little information is available in the literature comparing debagged and non-bagged fruit sunburn.…”

The Developmental Delay of Seedlings With Cotyledons Only Confers Stress Tolerance to Suaeda aralocaspica (Chenopodiaceae) by Unique Performance on Morphology, Physiology, and Gene Expression

“…The supernatant (1 ml) was added into a mixture of titanium sulfate [100 μl, 5% (w/v)] and ammonia (200 μl), and the precipitate that formed was washed to remove pigments and then dissolved in sulfuric acid (5 ml, 2 M). The absorbance was measured at 415 nm, and a calibration curve (0–100 μM of H 2 O 2 ) was prepared to determine the concentration (Wang et al, 2021a ). For malondialdehyde (MDA) concentration, seedlings (0.12 g) were ground into homogenate with trichloroacetic acid [TCA, 1 ml, 10% (w/v)] and centrifuged at 4,000 g for 10 min.…”