Permeability of Apricot Leaf Cuticle

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Abstract
A simple test method for quantitatively measuring the penetration of chemicals through leaf cuticle disks is described. Inclusion of a relatively non-penetrating marker dye in each replicate distinguishes between intact and defective disks and improves the precision of the method. Apricot leaf cuticle penetration follows the relationship PM1/2 = k(PC)n to the chloroform: water partition coefficient (PC) for the homologous series of methyl-,n-propyl-, and n-hexyl monosubstituted N-alkyl-[alpha]-chloroacetamides. A similar relationship is suggested for the homologous methyl and n-propyl disub-stituted derivatives, the major difference being in the value of k. Leaf cuticle penetration is a diffusion process influenced by temperature, concentration, and relative solubility in organic solvents. Although penetration can be increased markedly by lipophilic substituents, there are secondary effects which do not correlate with chloroform: water partitioning. Substitution itself, the presence of heteroatoms in the substi-tuent (chlorine, oxygen), and cyclization of the sidechain, do not increase (and may decrease) the rate of cuticle penetration to the degree suggested by the increased chloroform partitioning of the derivative. Un-saturation, olefinic or aromatic, does not affect the relationship greatly.

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