pH-dependent permeation of amino acids through isolated ivy cuticles is affected by cuticular water sorption and hydration shell size of the solute

Abstract

The permeabilities of amino acids for isolated cuticular membranes of ivy (Hedera helix L.) were measured at different pH. Cuticular permeances were lowest for the zwitterionic form at pH 6, followed by the cationic form at pH 1. Highest permeances were obtained for the anionic form at pH 11. Permeances were not correlated with octanol/water partition coefficients and decreased at a given pH with increasing molar volume of the solute. This finding suggests that permeation takes place in the polar cuticular pathways. The effect of pH on the cuticular transport properties was analysed according to the porous membrane model considering the polyelectrolytic character of the cuticle in terms of porosity, tortuosity, and size selectivity of the aqueous cuticular pathway which is altered by pH. An increase of water content and permeability of the cuticular membrane was caused by the dissociation of weak acidic groups with increasing pH leading to a swelling of the cuticle induced by fixed negative charges. In addition, the pH-dependent size of the hydration shell of the amino acids was identified as a secondary factor explaining the variability of cuticular permeances.

Cell Penetration, Herbicidal Activity, and in‐vivo‐Toxicity of Oligo‐Arginine Derivatives and of Novel Guanidinium‐Rich Compounds Derived from the Biopolymer Cyanophycin

“…Since it is known that oligo‐arginines penetrate plant cells very much the same way as other eukaryotic cells, it is possible that the low activity of both 1a ‐4 Glufos and 1a ‐4 Fos is instead due to poor foliar uptake. This is consistent with reports that very hydrophilic compounds cross a plant cuticle through a polar pathway that has molecular size limitations, which are likely incompatible with these large CPP‐salts …”

The permeation barrier of plant cuticles: uptake of active ingredients is limited by very long‐chain aliphatic rather than cyclic wax compounds

“…These blocks are removed by wax extraction, increasing the availability of polar pathways across the cuticle. 15,36 This study indicates that cyclic wax compounds do not contribute to the diffusion barrier for hydrophilic or lipophilic compounds. Therefore, the question arises, which selective advantages can be attributed to the, in many species significant, fraction of cyclic compounds, especially triterpenoids, present in the inner matrix of the cuticle?…”

“…These apparently contradictory findings can be reconciled by assuming that in the native cuticle, wax blocks some hydrophilic pathways before they reach the cuticular surface. These blocks are removed by wax extraction, increasing the availability of polar pathways across the cuticle …”

“…1). VLCA chain lengths ranged between C 29 and C 36 . n-Alkanes made up the major fraction of VLCAs (77%), followed by 23% alcohols (Table 1).…”

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.…”