Abstract
Cuticular wax covering the surface of fleshy fruit is closely related to fruit glossiness, development, and post-harvest storage quality. However, the information about formation characteristics and molecular mechanisms of cuticular wax in grape berry is limited. In this study, crystal morphology, chemical composition, and gene expression of cuticular wax in grape berry were comprehensively investigated. Morphological analysis revealed high density of irregular lamellar crystal structures, which were correlated with the glaucous appearances of grape berry. Compositional analysis showed that the dominant wax compounds were triterpenoids, while the most diverse were alkanes. The amounts of triterpenoids declined sharply after véraison, while those of other compounds maintained nearly constant throughout the berry development. The amounts of each wax compounds varied among different cultivars and showed no correlation with berry skin colors. Moreover, the expression profiles of related genes were in accordance with the accumulation of wax compounds. Further investigation revealed the contribution of cuticular wax to the water preservation capacity during storage. These findings not only facilitate a better understanding of the characteristics of cuticular wax, but also shed light on the molecular basis of wax biosynthesis in grape.
Highlights
Grape (Vitis vinifera) is an important fruit crop that is commonly grown worldwide [1]
Further investigation revealed the contribution of cuticular wax to the water preservation capacity during storage. These findings facilitate a better understanding of the characteristics of cuticular wax, and shed light on the molecular basis of wax biosynthesis in grape
By visual inspection of the berry surface of three representative grape cultivars, the entire surface of “Kyoho” and “Red Globe” berries appeared to be coated with a gentle glaucous waxy layer and the white frost gradually thicken as the berry developed; while the surface of “Shine Muscat” berries appeared glossy phenotype throughout the development stages (Figure 1A)
Summary
Grape (Vitis vinifera) is an important fruit crop that is commonly grown worldwide [1]. Cuticular wax is responsible for the whitish (glaucous) or glossy covering on the fruit, affecting the appearance quality and the market value of grape [2]. The hydrophobic properties of the cuticular wax have important roles in reducing non-stomatal water loss, protecting against ultraviolet radiation, and preventing pathogenic attacks during fruit development and storage [3]. The grape berry skin is impregnated with aliphatic and cyclic wax compounds [4]. The cyclic fraction usually contains triterpenoids of oleanolic acid and β-sitosterol, which exhibit numerous health beneficial properties including antioxidant, anticancer, anti-inflammatory, and anti-cardiovascular diseases [3, 5]. Research interest has been focused on the cuticular wax in grape due to their important roles in fruit quality and post-harvest storage properties
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