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. 2022 Jan 5:12:766602.
doi: 10.3389/fpls.2021.766602. eCollection 2021.

Building a Barrier: The Influence of Different Wax Fractions on the Water Transpiration Barrier of Leaf Cuticles

Pascal Seufert  1 , Simona Staiger  1 , Katja Arand  1 , Amauri Bueno  1 , Markus Burghardt  1 , Markus Riederer  1
Affiliations

Building a Barrier: The Influence of Different Wax Fractions on the Water Transpiration Barrier of Leaf Cuticles

Pascal Seufert et al. Front Plant Sci. .

Abstract

Waxes are critical in limiting non-stomatal water loss in higher terrestrial plants by making up the limiting barrier for water diffusion across cuticles. Using a differential extraction protocol, we investigated the influence of various wax fractions on the cuticular transpiration barrier. Triterpenoids (TRPs) and very long-chain aliphatics (VLCAs) were selectively extracted from isolated adaxial leaf cuticles using methanol (MeOH) followed by chloroform (TCM). The water permeabilities of the native and the solvent-treated cuticles were measured gravimetrically. Seven plant species (Camellia sinensis, Ficus elastica, Hedera helix, Ilex aquifolium, Nerium oleander, Vinca minor, and Zamioculcas zamiifolia) with highly varying wax compositions ranging from nearly pure VLCA- to TRP-dominated waxes were selected. After TRP removal with MeOH, water permeability did not or only slightly increase. The subsequent VLCA extraction with TCM led to increases in cuticular water permeabilities by up to two orders of magnitude. These effects were consistent across all species investigated, providing direct evidence that the cuticular transpiration barrier is mainly composed of VLCA. In contrast, TRPs play no or only a minor role in controlling water loss.

Keywords: leaf cuticles; leaf cuticular wax properties; non-stomatal transpiration; selective wax extraction; triterpenoids; very long-chain aliphatics; weighted average chain length.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Comparison of total cuticular loads of very long-chain aliphatics (VLCA) and triterpenoids (TRP) in selective wax extracts (purple) and full extracts (orange) of seven plant species. Data were normally distributed. Differences were tested using one-way ANOVA. Different letters stand for significant differences (p < 0.05) between the two extraction methods within a wax fraction. Columns show mean values and whiskers standard deviations (n = 4–8).
Figure 2
Figure 2
Comparison of cuticular wax compositions extracted from isolated cuticles with consecutive methanol (MeOH; blue) and chloroform (TCM; green) extraction steps. Normal distribution was found for data of all species except for the VLCA of both steps of V. minor and the VLCAs of the MeOH extraction of Z. zamiifolia. For normally distributed data, differences were tested for significance with one-way ANOVA. In all other cases, the Kruskal-Wallis test ANOVA with post-hoc Dunn’s test was used. Different letters stand for significant differences (p < 0.05) between the two extraction methods within a wax fraction. Columns show mean values and whiskers standard deviation (n = 4–8).
Figure 3
Figure 3
Chain length distribution of VLCA in the methanol (MeOH; blue) and the subsequent chloroform (TCM; green) extracts of seven plant species. Columns show mean values and whiskers standard deviation (n = 4–8).
Figure 4
Figure 4
Water permeability of isolated cuticles of seven plant species in untreated (CM; orange), methanol (M; blue), and subsequent chloroform (MX; green) extracted conditions. Investigation of significant differences was conducted by Kruskal-Wallis test ANOVA with post-hoc Dunn’s test. Boxes are interquartile ranges from 25 to 75%, whiskers 10–90% and dots designate outliers. Different letters stand for significant differences (p < 0.05) among treatments (p ≥ 28).
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