Penetration of Organic Compounds Through Isolated Cuticular Membranes with Special Reference to C Urea.

Studies of salute plenetration into living cells are becoming legion. Protective or barrier membranes must be traversed1. Cell particulates, cells themselves. and external plant surfaces are covered with membranes of varying permeabilities. Not the least among the membranes are the noncellular cuticles that cover all aerial plant parts including leaves. Absorption by living leaf cells of any foliar applied chemical (mineral nutrients, growth regulators. pesticides, antiliotics) must b)e preceded by transcuticular penetration (14). Some p&rneability. surface binding, and ion exchange characteristics have been report l for enzymically isolated cuticular membranes (16, 17). They include the stomatous green onion leaf cuticle an(l the astonmatous tomato fruit cuticle. Penetration through stomatous andl astomatous cuticles was much greater from the outer to the inner surface (influx ) than fromt the inner to the outer surface (efflux), more pronounce(l for cations than anions, and a function of the extent of ion binding on the surface opposite the site of initial entry. Ion exchange capacities of cuticular menbrane surfaces were greater for Ca+ + than for SO4--, and for green onion leaf cuticles than for those isolated from ripe tomato fruit. These observations suggested a study of the comparative rates of penetration and-I extent of cuticular surface binding of certain C14 labelled organic coIllpouncds with those already reporte(l for inorganic ions. Special attention was given urea which is commonly applied as a nutrient spray to some agricultural crops to provide nitrogen. The results of a few studies are also included for the plant growth inhibitors nialeic hydrazide an(l N,N-(imethylaniniosuccinlamllic acid. Organic molecules, because of their size, functional groups, and charge p)ose more complex problems than thle inorganic ions.