Size exclusion limits and lateral heterogeneity of the stomatal foliar uptake pathway for aqueous solutes and water‐suspended nanoparticles

Abstract

Penetration rates of foliar-applied polar solutes are highly variable and the underlying mechanisms are not yet fully understood. The contribution of stomata especially, is still a matter of debate. Thus, the size exclusion limits of the stomatal foliar uptake pathway, its variability and its transport capacity have been investigated. The size exclusion limits were analyzed by studying the penetration of water-suspended hydrophilic particles of two different sizes (43 nm or 1.1 microm diameter) into leaves of Vicia faba (L.). To avoid agglutination of the particles, plants were kept in water-saturated atmosphere. Penetration of the larger particles was never detected, whereas after 2 to 9 days, the smaller particles occasionally penetrated the leaf interior through stomatal pores. Permeability of stomata to Na(2)-fluorescein along the leaf blade of Allium porrum (L.) was highly variable and not correlated with the position on the leaf. When evaporated residues of the foliar-applied solutions were rewetted repeatedly, approximately 60% of the previously penetrated stomata were penetrated again. The average rate constant of penetration of an individual stoma was in the same order of magnitude as typical rate constants reported for the cuticular pathway. The observed sparseness of stomatal penetration together with its high lateral variability but local and temporal persistency was taken as evidence that stomata contributing to uptake differ from non-penetrated ones in the wettability of their guard cell cuticle. These results show that the stomatal pathway is highly capacitive because of its large size exclusion limit above 10 nm and its high transport velocity, but at the same time the high variability renders this pathway largely unpredictable.

No Evidence for Cerium Dioxide Nanoparticle Translocation in Maize Plants

“…The incorporation of nanoparticles into leaves has been reported earlier by Eichert et al who found that polymeric nanoparticles penetrated into the epidermis of Vicia faba (21). Corredor et al found nanoparticle penetration into the first cell layer of pumpkin plants (20).…”

“…Increasing the thickness of the biological barrier will therefore reduce the mobility of the nanoparticles and consequentially their ability for translocation. Uptake of nanoparticles into plant leaves has been proposed to occur through small pores in the cuticle (< 5 nm) or through stomatal apertures (21). Cell wall pores are smaller than ten nanometers and the cell wall is expected to be a tight sieve which does not allow nanoparticles migration (34).…”

“…However, particles of larger diameters (e.g. 1.1 µm) cannot enter leaves (21). Unfortunately, a quantitative description of the uptake processes has not been reported.…”

Improving the performance of calcium-containing spray formulations to limit the incidence of bitter pit in apple (Malus x domestica Borkh.)

“…The occurrence of epidermal structures in plant surfaces such as lenticels, stomata or trichomes may significantly influence the rate of absorption of surface-applied agrochemicals. While the significance of the stomatal pathway on the absorption of foliar sprays has been a matter of controversy for many years, recent evidence shows that it can largely contribute to the uptake process (Eichert et al, 2008).…”

Interactions between engineered nanomaterials and agricultural crops: implications for food safety

“…ENMs have the potential to penetrate leaf surfaces through stomatal pores (Eichert et al, 2008;Larue et al, 2014). Basipetal translocation of carbon-coated iron nanoparticles was evident from the epidermis of exposed Cucurbita mixta petioles; similarly, Ce was found in Cucumis sativus roots after leaf exposure to nanoparticulate CeO 2 (Corredor et al, 2009;Hong et al, 2014).…”