Size selectivity of aqueous pores in stomatous cuticles of Vicia faba leaves

Abstract

Size selectivity of aqueous pores in Vicia leaf cuticles was investigated by measuring the penetration of calcium salts into the abaxial surface of detached leaves. Molecular weights of salts ranged from 111 g mol(-1) to 755 g mol(-1). Penetration in light at 20 degrees C and 100% humidity was a first order process and rate constants of penetration ranged from 0.39 h(-1) (CaCl2) to 0.058 h(-1) (Ca-lactobionate). Penetration was a first order process in the dark as well, but the rate constants were smaller by a factor of 1.82. Plotting logarithmatised rate constants versus anhydrous molecular weights resulted in straight lines both in light and in the dark. The slopes per hour were very similar and the average slope was -1.2 x 10(-3) mol g(-1). Hence, size selectivity was not affected by stomatal opening, and in light or darkness permeability of Vicia cuticles decreased by a factor of 2.9 when molecular weight increased from 100 g mol(-1) to 500 g mol(-1). Silver nitrate was preferentially precipitated as silver chloride in guard cells, glandular trichomes and at the base of trichomes. It was concluded that these precipitates mark the location of aqueous pores in Vicia leaf cuticles. The size selectivity of aqueous pores in Vicia leaf cuticles is small compared to that observed in poplar leaf cuticles, in which permeability decreased by a factor of 7-13 for the same range of molecular weights. It is also much smaller than size selectivity of the lipophilic pathway in cuticles. These findings suggest that active ingredients of pesticides, growth regulators and chemical inducers with high molecular weights penetrate leaves at higher rates when formulated as ions.

Potential for foliar phosphorus fertilisation of dryland cereal crops: a review

“…Phosphorus formulations containing anionic species are not soluble in lipids as they are charged and cannot pass through the lipophilic pathway. Ionic species can only cross the lipid membrane if aqueous pores transverse the membrane (Schlegel et al 2005). Aqueous pores within the plant cuticle arise by hydration of permanent dipoles and ionic functional groups (Schönherr 2006).…”

AgCl precipitates in isolated cuticular membranes reduce rates of cuticular transpiration

“…However, it must be stated that prior to the transpiration experiments each single cuticle was checked for defects and holes allowing the penetration of liquid organic solvents by pipetting 50 ll ethanol on the outer surface. Microscopically small holes can easily be detected by this approach, since ethanol penetrates the CMs and diffraction of light is changed (Scho¨nherr and Schreiber In a recent study AgCl precipitates were analysed in intact Vicia faba leaves in order to trace preferential sites of uptake of polar compounds (Schlegel et al 2005). Two structures of the leaf surface of Vicia, trichomes and stomates, were preferentially stained.…”

Phyllosphere bacterial communities of trichome-bearing and trichomeless Arabidopsis thaliana leaves

“…The bases of trichomes, stomata, epidermal cell wall junctions and the grooves along veins were identified as areas most commonly and heavily colonized by epiphytic bacteria (Beattie and Lindow 1999). Current hypothesis holds that microbial growth is favoured at these sites because of increased water and nutrient availabilities (Leveau and Lindow 2001;Monier and Lindow 2004;Schlegel et al 2005). Trichomes may also exert a protective function by shielding epiphytic bacteria from UV radiation or by retaining water droplets (Jacobs and Sundin 2001).…”