Characterization of hydrophilic and lipophilic pathways of Hedera helix L. cuticular membranes: permeation of water and uncharged organic compounds

Abstract

The permeability of astomatous leaf cuticular membranes of Hedera helix L. was measured for uncharged hydrophilic (octanol/water partition coefficient log K(O/W) < or =0) and lipophilic compounds (log K(O/W) >0). The set of compounds included lipophilic plant protection agents, hydrophilic carbohydrates, and the volatile compounds water and ethanol. Plotting the mobility of the model compounds versus the molar volume resulted in a clear differentiation between a lipophilic and a hydrophilic pathway. The size selectivity of the lipophilic pathway was described by the free volume theory. The pronounced tortuosity of the diffusional path was caused by cuticular waxes, leading to an increase in permeance for the lipophilic compounds after wax extraction. The size selectivity of the hydrophilic pathway was described by hindered diffusion in narrow pores of molecular dimensions. A distinct increase in size selectivity was observed for hydrophilic compounds with a molar volume higher than 110 cm3 mol(-1). Correspondingly, the size distribution of passable hydrophilic pathways was interpreted as a normal distribution with a mean pore radius of 0.3 nm and a standard deviation of 0.02 nm. The increased permeance of the hydrophilic compounds by the removal of cuticular waxes was attributed to an increase in the porosity, a decrease in the tortuosity, and a widening of the pore size distribution. Cuticular transpiration resulted from the permeation of water across the hydrophilic pathway. The far-reaching implications of two parallel pathways for the establishment of correlations between cuticular structure, chemistry, and function are discussed.

Localization of the Transpiration Barrier in the Epi- and Intracuticular Waxes of Eight Plant Species: Water Transport Resistances Are Associated with Fatty Acyl Rather Than Alicyclic Components

“…The first part of this model is based on the finding that the majority of water molecules are absorbed into and cross through the cuticular wax (as opposed to larger, polar solutes that pass through a limited number of aqueous channels extending from the epidermal cell wall to the tissue surface; Riederer and Schreiber, 2001;Schönherr and Schreiber, 2004;Beyer et al, 2005;Popp et al, 2005;Schreiber, 2005;Schönherr, 2006;Weichert and Knoche, 2006;Arand et al, 2010). The epicuticular wax film must consequently impose a resistance on water movement, and this resistance acts in series with the resistance(s) imposed on inner pathway sections.…”

Abscisic Acid Deficiency Causes Changes in Cuticle Permeability and Pectin Composition That Influence Tomato Resistance to Botrytis cinerea

“…ABA Deficiency Leads to a Decrease in Surface Hydrophobicity and Leaf Trichome Number Cuticular permeability to watery solutions and hydrophilic compounds is known to be correlated with wax amounts and composition (Hauke and Schreiber, 1998;Popp et al, 2005). Furthermore, wax amounts and the relative composition of the hydrocarbon, alcohol, and aldehyde fractions of the cuticular wax determine the hydrophobicity of the leaf surface (Bringe et al, 2006;Koch and Ensikat, 2007).…”

The Developmental Pattern of Tomato Fruit Wax Accumulation and Its Impact on Cuticular Transpiration Barrier Properties: Effects of a Deficiency in a β-Ketoacyl-Coenzyme A Synthase (LeCER6)

“…Even Haas (1974) argued that predominantly epi-and intracuticular waxes are responsible for the observed reduction of cuticular water permeability during the course of fruit growth and ripening. With regard to the hydrophilic pathway, cuticular waxes might block potential polar paths and the removal of waxes might increase the pore area or decrease the tortuosity of the hydrophilic pathway, thereby increasing water permeability (Popp et al, 2005). Chloroform extraction of astomatous pear leaf cuticular membranes, however, resulted in only 2-to 3-fold increased rates of penetration for calcium chloride, being restricted to the polar pathway.…”

“…Although cuticular membranes are mainly considered as a lipid barrier, hydrophilic structures like nonesterified hydroxyl and carboxyl groups within the cutin polymer (Schö nherr and Huber, 1977) and polysaccharides like pectin and cellulose (Jeffree, 1996) are also present. Currently, two parallel and independent pathways for diffusion across the plant cuticle are discussed: (1) a lipophilic pathway accessible for nonionic lipophilic molecules composed of lipophilic cutin and wax domains; and (2) a polar pathway open to inorganic ions and small uncharged and charged organic molecules, which is postulated to consist of a continuum of polar materials across the cuticle (Popp et al, 2005;Schönherr, 2006;Schreiber, 2006). There is evidence that water as a small uncharged polar molecule may have access to both pathways of transport (Schö nherr and Merida, 1981; Niederl et al, 1998;Riederer and Schreiber, 2001;Schlegel et al, 2005;Riederer, 2006).…”