Structure of the cuticular transpiration barrier: role of epicuticular wax

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The leaf atmosphere interface is formed by the plant cuticle covering all outer epidermal cell walls. The cuticle is an extracellular lipophilic biopolymer. It is composed of cutin and cuticular wax deposited in the cutin polymer (intracuticular wax) and on the outer surface (epicuticular wax). It is well known that cuticular wax is mainly establishing the transpiration barrier of the cuticle, since upon wax extraction cuticular permeability increases by 2-3 orders of magnitude. Often formation and appearance of epicuticular wax is significantly affected by environmental influences and it is normally assumed that this affects the transpiration barrier. However, it is still unknown to what extent epicuticular wax contributes to the formation of the transpiration barrier. In the research project suggested here, a verified method, measuring cuticular water permeability of 3H2O before and after the selective removal of epicuticular wax from the cuticle surface, will be used. Verification and quantification of successful wax removal will be done in parallel by scanning electron microscopy, gas chromatography and mass spectrometry. This combined approach should ultimately allow answering the long-lasting question whether epicuticular wax contributes to the formation of the cuticular transpiration barrier or not?