Composition and Physiological Function of the Wax Layers Coating Arabidopsis Leaves: β-Amyrin Negatively Affects the Intracuticular Water Barrier    

Abstract

Plants prevent dehydration by coating their aerial, primary organs with waxes. Wax compositions frequently differ between species, organs, and developmental stages, probably to balance limiting nonstomatal water loss with various other ecophysiological roles of surface waxes. To establish structure-function relationships, we quantified the composition and transpiration barrier properties of the gl1 mutant leaf waxes of Arabidopsis (Arabidopsis thaliana) to the necessary spatial resolution. The waxes coating the upper and lower leaf surfaces had distinct compositions. Moreover, within the adaxial wax, the epicuticular layer contained more wax and a higher relative quantity of alkanes, whereas the intracuticular wax had a higher percentage of alcohols. The wax formed a barrier against nonstomatal water loss, where the outer layer contributed twice as much resistance as the inner layer. Based on this detailed description of Arabidopsis leaf waxes, structure-function relationships can now be established by manipulating one cuticle component and assessing the effect on cuticle functions. Next, we ectopically expressed the triterpenoid synthase gene AtLUP4 (for lupeol synthase4 or b-amyrin synthase) to compare water loss with and without added cuticular triterpenoids in Arabidopsis leaf waxes. b-Amyrin accumulated solely in the intracuticular wax, constituting up to 4% of this wax layer, without other concomitant changes of wax composition. This triterpenoid accumulation caused a significant reduction in the water barrier effectiveness of the intracuticular wax.

Nutrient Changes and in Vitro Digestibility in Generative Stage of M10-BMR Sorghum Mutant Lines

“…This coating material may prevent water loss during transpiration. Wax material is insoluble in ether leading to a higher crude fat contained in forage material (Buschhaus & Jetter, 2012). The general result showed that EE increased with the increased generative stage.…”

Apoplastic Diffusion Barriers in Arabidopsis

“…A detailed quantitative chemical analysis of leaf wax and a corresponding functional analysis of the water barrier properties of the cuticles of the Arabidopsis glabra1 (gl1) (At3g27920) mutant were recently performed (Buschhaus and Jetter, 2012). This study demonstrated that the upper (adaxial) and lower (abaxial) leaf surfaces differed in their wax loads and had distinct wax compositions.…”

The Formation and Function of Plant Cuticles

“…Specific compound classes appear to be associated with water barrier properties of the cuticle; notably, the more nonpolar components, such as alkanes, tend to be associated with decreased CWP, while nonaliphatic wax compounds, such as triterpenoids, are likely a less effective water barrier (Leide et al, 2007;Buschhaus and Jetter, 2012). This is consistent with a model in which cuticular waxes localize within either crystalline or amorphous domains of the cuticle, with aliphatic compounds forming crystallite "rafts" that are impervious to water, forcing water, and other polar metabolites, to diffuse by a circuitous route through the amorphous domains that are formed by more polar and cyclic waxes (Riederer and Schreiber, 1995).…”