Journal
AOB PLANTS
Volume 8, Issue -, Pages -Publisher
OXFORD UNIV PRESS
DOI: 10.1093/aobpla/plw027
Keywords
Aliphatic compounds; cuticular transpiration; cuticular wax; cutin; desert; minimum conductance; plant cuticle; temperature; transition temperature; triterpenoids
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Funding
- National Plan for Science, Technology and Innovation (MAARIFAH), King Abdulaziz City for Science and Technology, Kingdom of Saudi Arabia [12-ENV2564-02]
- Capes Foundation, Ministry of Education of Brazil [8908-13-3]
- Chinese Academy of Sciences Visiting Professorship for Senior International Scientists [2011T2S31]
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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 (g(min)) as a proxy for cuticular water permeability. g(min) of R. stricta (5.41 x 10 x 5 m s(-1) at 25 degrees 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 degrees C) on g(min) (2.4-fold) is lower than in all other species (up to 12-fold). Rhazya stricta is also special since the temperature dependence of g(min) 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 mu g 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.
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