Cuticle and skin cell walls have common and unique roles in grape berry splitting

Ben-Min Chang,Markus Keller

doi:10.1038/s41438-021-00602-2

Abstract

The skin protects a fruit from environmental stresses and supports the fruit’s structure. Failure of the skin leads to fruit splitting and may compromise commercial production for fruit growers. The mechanical properties of the cuticle and skin cell walls might influence the splitting susceptibility of fleshy fruits. Thin shell theory and fracture mechanics were utilized in this study to target the potential factors contributing to splitting susceptibility. The study analyzed the structure of the cuticle and epidermis in ripening grape berries and examined the temporal dynamics of berry splitting. Cuticular waxes were partially removed, and skin cell walls were manipulated using wall stiffening and loosening solutions that altered reactions involving hydrogen peroxide. A more than twofold difference in cuticle thickness among grape cultivars did not account for their differences in splitting resistance. However, while removing predominantly epicuticular wax did not alter the berries’ splitting resistance, their surface appearance and increasing yield strength following partial wax removal support the notion that cuticular waxes contribute to berry mechanical properties. Immersing berries in H2O2-based cell wall loosening solutions increased the splitting probability and accelerated berry splitting, whereas cell wall stiffening solutions decreased the splitting probability and delayed berry splitting. These results showed that both cuticle and skin cell walls contribute to the mechanical properties of grape berries and to their splitting resistance. The results also suggest that the two current explanations for fruit splitting, the critical turgor model and the zipper model, should be viewed as complementary rather than incompatible.

Highlights

The skin is the thin outer layer of a fleshy fruit, and it is made up of the composite cuticle, the epidermis, and the hypodermis[1,2]
We compared green hard (GH) berries and overripe (OR) berries to determine whether any differences observed in mature berries were already present in immature berries, i.e., before the start of ripening
The present study demonstrated that the fruit cuticle and skin cell walls have both common and unique roles in grape berry splitting

Summary

Introduction

The skin (exocarp) is the thin outer layer of a fleshy fruit, and it is made up of the composite cuticle, the epidermis, and the hypodermis[1,2]. The matrix is a network of cutin imbued with waxes. In fruit, this extracellular membrane provides protection from biotic or abiotic stresses and helps the fruit to ripen successfully to disperse the seeds for reproducing the generation[3]. In addition to its protective role, the skin limits fruit growth[5]. May jeopardize the integrity of the cuticle and/or skin[6]. Existing microcracks in the cuticle can extend to become cracks in the fruit skin. Grape (Vitis spp.) berries, like other fleshy fruits, are susceptible to splitting. The driving forces for berry splitting include excessive internal pressure[8,9,10], excessive surface-water absorption[11], or physical damage, e.g. by insects or birds[12]

Objectives

Methods

Results

Conclusion