Cuticular waxes on Arabidopsis thaliana close relatives Thellungiella halophila and Thellungiella parvula

Thellungiella halophila and Thellungiella parvula have been recently reported to be close halophytic relatives of Arabidopsis thaliana. Crystallization patterns and chemical composition of stem and leaf cuticular waxes on T. halophila, T. parvula, and A. thaliana ecotype C24 were examined. Whereas the heavy glaucousness, total wax amounts, wax crystal structures, and wax chemical constituents on inflorescence stems of these species were similar, their leaf waxes differed significantly. Arabidopsis thaliana leaf surfaces were glossy, whereas T. parvula leaf surfaces were glaucous throughout development. By comparison, T. halophila leaf surfaces were glossy before flower initiation but glaucous after. Glaucousness resulted from the presence of densely distributed epicuticular wax crystals visible with electron microscopy. Glaucous leaves of both T. halophila and T. parvula produced 12.7- and 24.1-fold more total wax, respectively, than leaves of A. thaliana. Waxes on glossy leaves of T. halophila were greatly enriched in free acids relative to waxes on glossy leaves of A. thaliana. Glaucous leaves of T. halophila and T. parvula had similar wax composition and wax crystallization patterns as their respective stems, except total wax quantity was lower on leaves. As did glaucous stems, glaucous leaves produced relatively large amounts of secondary alcohols and ketones, constituents barely detectable on glossy leaves. Our results indicate that T. halophila and T. parvula may provide, via the application of genomics approaches recently developed for A. thaliana, valuable model systems for isolating genes involved in leaf wax synthesis and the regulation of leaf and stem wax specificity.