Developmental pattern of grapevine (Vitis vinifera L.) berry cuticular wax: Differentiation between epicuticular crystals and underlying wax.

Katja Arand,Evi Bieler,Hanns-Heinz Kassemeyer,Markus Dürrenberger,Hernâni Gerós

doi:10.1371/journal.pone.0246693

Abstract

The grapevine berry surface is covered by a cuticle consisting of cutin and various lipophilic wax compounds. The latter build the main barrier for transpirational water loss and protect the fruit against environmental factors e.g. pests, mechanical impacts or radiation. The integrety of the fruit surface is one important key factor for post-harvest quality and storage of fruits. Nonetheless, the developmental pattern of cuticular wax was so far only investigated for a very limited number of fruits. Therefore, we performed comparative investigations on the compositional and morphological nature of epicuticular wax crystals and underlying wax during fruit development in Vitis vinifera. The main compound oleanolic acid belongs to the pentacyclic triterpenoids, which occur very early in the development in high amounts inside the cuticle. The amount increases until veraison and decreases further during ripening. In general, very-long chain aliphatic (VLCA) compounds are present in much smaller amounts and alcohols and aldehydes follow the same trend during development. In contrast, the amount of fatty acids constantly increases from fruit set to ripening while wax esters only occur in significant amount at veraison and increase further. Wax crystals at the fruit surface are solely composed of VLCAs and the morphology changes during development according to the compositional changes of the VLCA wax compounds. The remarkable compositional differences between epicuticular wax crystals and the underlying wax are important to understand in terms of studying grape-pest interactions or the influence of environmental factors, since only wax crystals directly face the environment.

Highlights

The outer layer of fleshy fruits, such as berries, fulfils a multiple function as an interface between the fruit containing the seed with the developing embryo and the environment
The hydrophobic properties of the wax coating have a crucial function as a preformed barrier that protects the berry from uncontrolled water loss and other environmental factors like pathogens and herbivore attack [11, 12]
There is good evidence that the cuticular transpiration barrier is preferentially associated with very-long chain aliphatic wax compounds [3, 13], while triterpenoids contribute to the mechanical strength [14], heat stability [15] or biological activity [16] of the cuticle

Summary

Introduction

The outer layer of fleshy fruits, such as berries, fulfils a multiple function as an interface between the fruit containing the seed with the developing embryo and the environment. During the development of the grape berry, the volume increases about 300-fold In this growth process, the skin of the berries has an important function as a containment of the pericarp since the integrity of the surface must be maintained [1, 2]. The matrix of the cuticle is built by a three-dimensional network preferentially composed of polymerized C16 and C18 hydroxy fatty acids [3] It is impregnated with aliphatic and cyclic wax components. To visualize the highly sensitive micro and nanostructure of the epicuticular wax, we used cryo-scanning electron microscopy This tool enables to detect finest differences in the structure of the wax crystals which would completely disappear during the fixation process for TEM analysis. The scientific results of this work represent significant achievements for targeted breeding of grapevine cultivars with resistance to pests and pathogens and higher berry resilience to environmental changes

Methods

Results

Conclusion