Cuticular permeability of the three tree speciesPrunus IaurocerasusL.,Ginkgo bilobaL. andJuglans regiaL.: comparative investigation of the transport properties of intact leaves, isolated cuticles and reconstituted cuticular waxes
Cuticular transport properties of intact leaves, isolated cuticular membranes and reconstituted cuticular waxes of the three tree species Prunus laurocerasus L., Ginkgo biloba L. and Juglans regia L. were measured using six different 14C-labelled compounds, benzoic acid, salicylic acid, 2,4-dichlorophenoxy acid, metribuzin, 4-nitrophenol, and atrazine. For the same compound and the same species, the permeance of the intact leaf and the isolated cuticle was equal. This provides strong evidence demonstrating that transport properties of cuticles are not altered during isolation. Additionally, diffusion coefficients of the 14C-labelled compounds in isolated and subsequently reconstituted cuticular wax of the three tree species were measured. Permeances of intact leaves and isolated cuticles could be predicted from diffusion coefficients, wax/water partition coefficients and the thickness of the transport-limiting wax layer with a mean deviation of about 1.7. This provides evidence that transport properties of recrystallized cuticular waxes do indeed reflect barrier properties of isolated cuticular membranes and intact leaves with in situ waxes. Thus, it can be concluded that the investigation of cuticular permeability using the three independent experimental systems of different complexity give comparable results. Finally, it was observed that permeances and diffusion coefficients measured with P. laurocerasus were always significantly lower than those measured with G. biloba and J. regia. This is interpreted as an ecological adaptation of the respective species. The evergreen species P. laurocerasus must be more adapted to environmental stress such as drought and frost injury compared to the two deciduous species G. biloba and J. regia.