Localization of the Transpiration Barrier in the Epi- and Intracuticular Waxes of Eight Plant Species: Water Transport Resistances Are Associated with Fatty Acyl Rather Than Alicyclic Components

Abstract

Plant cuticular waxes play a crucial role in limiting nonstomatal water loss. The goal of this study was to localize the transpiration barrier within the layered structure of cuticles of eight selected plant species and to put its physiological function into context with the chemical composition of the intracuticular and epicuticular wax layers. Four plant species (Tetrastigma voinierianum, Oreopanax guatemalensis, Monstera deliciosa, and Schefflera elegantissima) contained only very-long-chain fatty acid (VLCFA) derivatives such as alcohols, alkyl esters, aldehydes, and alkanes in their waxes. Even though the epicuticular and intracuticular waxes of these species had very similar compositions, only the intracuticular wax was important for the transpiration barrier. In contrast, four other species (Citrus aurantium, Euonymus japonica, Clusia flava, and Garcinia spicata) had waxes containing VLCFA derivatives, together with high percentages of alicyclic compounds (triterpenoids, steroids, or tocopherols) largely restricted to the intracuticular wax layer. In these species, both the epicuticular and intracuticular waxes contributed equally to the cuticular transpiration barrier. We conclude that the cuticular transpiration barrier is primarily formed by the intracuticular wax but that the epicuticular wax layer may also contribute to it, depending on species-specific cuticle composition. The barrier is associated mainly with VLCFA derivatives and less (if at all) with alicyclic wax constituents. The sealing properties of the epicuticular and intracuticular layers were not correlated with other characteristics, such as the absolute wax amounts and thicknesses of these layers.

The permeation barrier of plant cuticles: uptake of active ingredients is limited by very long‐chain aliphatic rather than cyclic wax compounds

“…To the authors' knowledge, similar studies testing the effects of VLCA and cyclic wax fractions on organic solute permeability of cuticles have not been reported to date. The results here, however, agree with the finding by Jetter and Riederer that in eight species, the fatty acyl wax fraction was associated with cuticular water permeability . Another study proposed the hypothesis that cyclic compounds in tomato fruit cuticles do not constitute the permeation barrier to water …”

“…The waxes associated with the plant cuticle impregnate the cutin matrix (intracuticular waxes) and are deposited on the outer surface as a thin film (epicuticular waxes), sometimes together with epicuticular wax crystals . Previous studies have demonstrated that the epicuticular wax of the plant species investigated consisted of VLCAs, whereas the cyclic fraction was located exclusively in the interior of the cutin matrix . Treating the intact adaxial surface of leaves of P. laurocerasus with methanol did not release any triterpenoids, proving that the cyclic compounds are located in the inner layers of the cuticle and are effectively shielded from the extractive action of methanol by a superficial layer of VLCAs (Fig.…”

“…Cuticular waxes are embedded within the cutin and also occur as epicuticular wax crystals or films deposited on the cuticular surface . Cuticular waxes are composed of very long‐chain aliphatic compounds (VLCAs) and cyclic substances such as pentacyclic triterpenoids, sterols and tocopherols . VLCAs consist mainly of primary n ‐alcohols, n ‐alkanes, fatty acids and alkyl esters.…”

TaCER1‐1A is involved in cuticular wax alkane biosynthesis in hexaploid wheat and responds to plant abiotic stresses

“…The waxes are embedded into the polymer matrix and deposited onto its surface (Buschhaus & Jetter, 2011), to protect the tissue against adverse abiotic and biotic conditions (Jetter & Riederer, 2016;Müller, 2006;Reina-Pinto & Yephremov, 2009). Wax compositions and transpiration barrier properties vary widely between species (Jetter & Riederer, 2016), likely due to fine-tuned differences in the underlying biosynthetic machineries.…”

Differences in monoterpene emission characteristics after ozone exposure between three clones representing major gene pools of <I>Cryptomeria japonica</I>

“…might increase if the wax layers are degraded. Jetter and Riederer 2016 reported that the sealing properties of the cuticular were not correlated with the absolute wax amount and thickness of wax layers, but it is maintained by the existence of the layer containing very long chain fatty acid. Barnes et al 1988 investigated the effect of O 3 fumigation on the condition of the epicuticular wax of Norway spruce using scanning electron microscopy SEM .…”