Specific characteristics of the apple fruit cuticle: Investigation of early and late season cultivars ‘Prima’ and ‘Florina’ ( Malus domestica Borkh.)

Abstract

Abstract The cuticle is a heterogeneous extracellular layer, whose composition varies between plant species, cultivars and organs. Specific structural and compositional characteristics indicate the domesticated apple (Malus domestica Borkh.) as a suitable non-model plant system for comprehensive analyses of the cuticularization of epidermal cell walls. Our findings focused on the cuticular deposition of apple fruits, offering a continuous, thick and robust but also lenticel-containing experimental system for functional studies. In detail, the cuticular wax and cutin composition and the water permeance of apple fruits were comparatively analyzed in two cultivars, which also demonstrates the cultivar-specific plasticity of cuticle formation. Despite significant differences in cuticle thickness and weight, fruits of the early and late season apple cultivars ‘Prima’ and ‘Florina’ accumulated on average 95 μg cm−2 cuticular waxes mainly consisting of pentacyclic triterpenoids like ursolic acid (≥70%). The average chain length of the aliphatic wax fraction of ‘Florina’ and ‘Prima’ was about 29.1. The cutin matrix averaged 995 μg cm−2 dominated by hydroxylated hexadecanoic and octadecanoic acid monomers (mixed C16/C18 type). Although the hydrophobic cuticle is the main barrier in limiting transpirational water loss across the outermost plant surface, chemical differences between both cultivars were not related to the water permeance. ‘Prima’ and ‘Florina’ fruit surfaces had an average permeance for water of 5 × 10−5 m s−1. It is hypothesized that compositional differences such as a higher amount of alkanoic acids, primary alkanols and alkanals in the cuticular wax mixture and modifications in the cutin matrix in the late season cultivar ‘Florina’ compared to early season cultivar ‘Prima’ represent cultivar-specific patterns in cuticle formation of apple fruits.