Penetration of Stomata by Liquids

Abstract

Wettability of the leaf surface, surface tension of the liquid, and stomatal morphology control penetration of stomata by liquids. The critical surface tension of the lower leaf surface of Zebrina purpusii Bruckn. was estimated to be 25 to 30 dyne cm-'. Liquids having a surface tension less than 30 dyne cm'i gave zero contact angle on the leaf surface and infiltrated stomata spontaneously while liquids having a surface tension greater than 30 dyne cm-' did not wet the leaf surface and failed to infiltrate stomata. Considering stomata as conical capillaries, we were able to show that with liquids giving a finite contact angle, infiltration depended solely on the relationship between the magnitude of the contact angle and the wall angle of the aperture. Generally, spontaneous infiltration of stomata will take place when the contact angle is smaller than the wall angle of the aperture wall. The degree of stomatal opening (4, 6, 8, or 10 /m) was of little importance.Cuticular ledges present at the entrance to the outer vestibule and between the inner vestibule and substomatal chamber resulted in very small if not zero wall angles, and thus played a major role in excluding water from the intercellular space of leaves. We show why the degree of stomatal opening cannot be assessed by observing spontaneous infiltration of stomata by organic liquids of low surface tension.tionship between any of these parameters and penetration has been generally poor. In this paper we present a systematic assessment of stomatal penetration by liquids based on the theory of capillary rise. THEORY When a liquid enters a capillary of circular cross-section the pressure difference (P) across the liquid meniscus is represented by equation 1,where '/L represents the surface tension of the liquid and R, and RI the principal radii of curvature of the liquid meniscus (1). In a narrow cylindrical capillary the meniscus is a segment of a sphere; R, and R, are equal and can be expressed in terms of the advancing contact angle (09) (4,22,27) unless external pressure is applied (6, 7). Some organic liquids, however, are known to penetrate readily, which led to attempts to estimate the degree of stomatal opening from substomatal penetration of certain organic liquids (18,22,25). Reports concerned with the effect of surfactants on promoting penetration into stomata and the substomatal space by aqueous solutions are contradictory (3, 4. 11, 14). Surface tension, viscosity, contact angle, diameter of the stomatal aperture, final height and initial velocity of capillary rise have been implicated in controlling penetration of liquids into the stomatal pore and substomatal chamber (4,6,7,18,26,27) A liquid will rise in the capillary spontaneously only if P is positive. The sign of P is determined by the term cos O.,; P being positive when OA < 90', zero when 9A = 900 and negative when O., > 900. The magnitude of P increases as r decreases.For a conical capillary (Fig. 1)

Developmental Changes in Leaf Epicuticular Waxes in Relation to Foliar Penetration

“…Although, Sands and Bachelard (1973b) suggest that uptake of picloram into leaves of Eucalyptus spp. proceeds via stomatal infiltration, it is generally accepted that the stomatal route of penetration can only be exploited for aqueous formulations when the surface tension is reduced below 30 mN m^^ (Schonherr and Bukovac, 1972). Since, for the present experiments, surface tension (46 mN m"^) greatly exceeded this minimum value, it seems more likely that the higher rates of uptake into the abaxial leaf surface of these species is associated with increased penetration into the guard and accessory cells.…”

Wettability, Polarity, and Water Absorption of Holm Oak Leaves: Effect of Leaf Side and Age

“…In the case of holm oak adaxial leaf surfaces, trichomes and the remaining scars after trichome shedding may play a key role in water absorption. The high surface tension, polarity, and H-bonding capacity of water theoretically pose restrictions for the penetration of this liquid through the cuticle (Guzmán et al, 2014(Guzmán et al, a, 2014b and also via stomata (Schönherr and Bukovac, 1972;Burkhardt et al, 2012). The actual contribution of leaf trichomes to the absorption of water and solutes remains unclear (Fernández et al, 2014).…”

Effects of Surfactants on Propanil Penetration through Adaxial Epidermis of <i>Commelina communis</i>

“…Especially for stomatal penetration, spray solution should have very low surface tension and a good wetting characteristic to treat particular weeds. 26,27) In the solution/membrane/water system, the membrane surface is already completely wet, and surfactants cannot make it any wetter. 28, 29) In our test, however, a nonionic surfactant was most effective on propanil penetration, and two ionic surfactants promoted penetration about two times when the initial penetration rate was low (Table 2).…”