Abstract
This study assessed the primary impacts of exogenous melatonin (MT) treatment on grape berry metabolism. Exogenous MT treatment increased the endogenous MT content and modified berry ripening. Transcriptomic analysis revealed that the processes of polyphenol metabolism, carbohydrate metabolism and ethylene biosynthesis and signaling were the three most significantly altered biological processes upon MT treatment. Further experiments verified that MT treatment increased the contents of total anthocyanins, phenols, flavonoids and proanthocyanidins in berries. Additionally, the contents of 18 of the 22 detected individual phenolic compounds were enhanced by MT treatment; particularly, the resveratrol content was largely increased concomitantly with the up-regulation of STS gene expression. Meanwhile, MT treatment enhanced the antioxidant capacity of berries. On the other hand, it was indicated that ethylene participated in the regulation of polyphenol metabolism and antioxidant capacity under MT treatment in grape berries. In summary, MT enhances the polyphenol content and antioxidant capacity of grape berries partially via ethylene signaling.
Highlights
Grapes (Vitis vinifera L) are one of the world’s largest fruit crops, with an annual production of more than 60 million metric tons
In a different experiment conducted in 2016, the same MT treatments as in 2015 were applied to determine statistical effects of year, MT treatment and their interaction on polyphenol content and antioxidant capacity; 100 μM MT, 100 μM MT + 5 μl.l−1 1-MCP + 0.1% NiCl2 (w/v), and 100 μM ACC were applied at onset of veraison, and the berries were collected at 3 and 60 days after the first MT treatment (DAT) to determine the role of ethylene in mediating MT signaling
The enhancement of antioxidant capacity induced by MT is associated with the increased endogenous MT and polyphenolic constituents and with their complicated reactions. This is the first report to elucidate that polyphenol metabolism is the most predominant biological process in response to MT treatment in grape berries in the light of RNA-Seq analysis
Summary
Grapes (Vitis vinifera L) are one of the world’s largest fruit crops, with an annual production of more than 60 million metric tons. 71% of world grape production is used for wine, 27% as fresh fruit, and 2% as dried fruit. Grapes and other fruits, such as apples, tomatoes, and so on, contain natural MT (Arnao and Hernández-Ruiz, 2014). MT has been shown to occur in all grape berry tissues (skin, flesh, and seeds) as well as in wine (Murch et al, 2010; Vitalini et al, 2011). Its concentration depends on the grape cultivar and the phenological stage; the highest concentration of MT in the vineyard occurs at Melatonin Enhances Polyphenol Accumulation the early stage of veraison in wine grapes (Murch et al, 2010). Some studies indicate the role of MT in plants as a growth regulator and/or biostimulator (Arnao and Hernández-Ruiz, 2015). MT can affect root development by regulating auxin synthesis, transport and signaling in Arabidopsis and tomato (Wang et al, 2016; Wen et al, 2016), promote seed germination by regulating the biosynthesis and catabolism of ABA and GA4 in cucumber (Zhang et al, 2014), promote tomato ripening (Sun et al, 2015), and increase the size and synchronicity of grape berries (Meng et al, 2015)
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