title: Effectiveness of cuticular transpiration barriers in a desert plant at controlling water loss at high temperatures.
abstract: Maintaining the integrity of the cuticular transpiration barrier even at elevated temperatures is of vital importance especially for hot-desert plants. Currently, the temperature dependence of the leaf cuticular water permeability and its relationship with the chemistry of the cuticles are not known for a single desert plant. This study investigates whether (i) the cuticular permeability of a desert plant is lower than that of species from non-desert habitats, (ii) the temperature-dependent increase of permeability is less pronounced than in those species and (iii) whether the susceptibility of the cuticular permeability barrier to high temperatures is related to the amounts or properties of the cutin or the cuticular waxes. We test these questions with Rhazya stricta using the minimum leaf water vapour conductance (gmin) as a proxy for cuticular water permeability. gmin of R. stricta (5.41 × 10(-5) m s(-1) at 25 °C) is in the upper range of all existing data for woody species from various non-desert habitats. At the same time, in R. stricta, the effect of temperature (15-50 °C) on gmin (2.4-fold) is lower than in all other species (up to 12-fold). Rhazya stricta is also special since the temperature dependence of gmin does not become steeper above a certain transition temperature. For identifying the chemical and physical foundation of this phenomenon, the amounts and the compositions of cuticular waxes and cutin were determined. The leaf cuticular wax (251.4 μg cm(-2)) is mainly composed of pentacyclic triterpenoids (85.2% of total wax) while long-chain aliphatics contribute only 3.4%. In comparison with many other species, the triterpenoid-to-cutin ratio of R. stricta (0.63) is high. We propose that the triterpenoids deposited within the cutin matrix restrict the thermal expansion of the polymer and, thus, prevent thermal damage to the highly ordered aliphatic wax barrier even at high temperatures.
authors.affiliation: Chair of Botany II - Ecophysiology and Vegetation Ecology, University of Würzburg, Julius-von-Sachs-Pl. 3, Würzburg D-97082, Germany.
authors.forename: Ann-Christin
authors.initials: AC
authors.lastname: Schuster
authors.affiliation: Chair of Botany II - Ecophysiology and Vegetation Ecology, University of Würzburg, Julius-von-Sachs-Pl. 3, Würzburg D-97082, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Burghardt
authors.affiliation: Department of Botany and Microbiology, College of Science, King Saud University, PO Box 2455, Riyadh 11451, Saudi Arabia.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Alfarhan
authors.affiliation: Chair of Botany II - Ecophysiology and Vegetation Ecology, University of Würzburg, Julius-von-Sachs-Pl. 3, Würzburg D-97082, Germany.
authors.forename: Amauri
authors.initials: A
authors.lastname: Bueno
authors.affiliation: Chair of Botany I - Plant Physiology and Biophysics, University of Würzburg, Julius-von-Sachs-Pl. 2, Würzburg D-97082, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Hedrich
authors.affiliation: Chair of Botany II - Ecophysiology and Vegetation Ecology, University of Würzburg, Julius-von-Sachs-Pl. 3, Würzburg D-97082, Germany.
authors.forename: Jana
authors.initials: J
authors.lastname: Leide
authors.affiliation: Department of Botany and Microbiology, College of Science, King Saud University, PO Box 2455, Riyadh 11451, Saudi Arabia.
authors.forename: Jacob
authors.initials: J
authors.lastname: Thomas
authors.affiliation: Chair of Botany II - Ecophysiology and Vegetation Ecology, University of Würzburg, Julius-von-Sachs-Pl. 3, Würzburg D-97082, Germany riederer@uni-wuerzburg.de.
authors.forename: Markus
authors.initials: M
authors.lastname: Riederer
keywords: Aliphatic compounds; cuticular transpiration; cuticular wax; cutin; desert; minimum conductance; plant cuticle; temperature; transition temperature; triterpenoids