Permeation characteristics of isolated cuticles of Citrus aurantium L. for monoterpenes

Summary

Permeation parameters of isolated cuticular membranes of Citrus aurantium L. for gaseous monoterpenes were determined by an isostatic system. For α-pinene and d-limonene permeability coefficients range from 4.3 × 10⁻¹¹ m⁻² s⁻¹ to 7.3 × 10⁻¹¹ m⁻² s⁻¹. These values can be compared to that measured for benzene gas at the cuticle of Citrus. The permeability coefficients of the two monoterpenes did not differ significantly, in contrast to their diffusioin coefficients. The diffusion coefficient values are 3.7 × 10⁻¹⁵ m⁻² s⁻¹ for limonene and 15.5 × 10⁻¹⁵ m⁻² s⁻¹ for α-pinene. The reason for this difference is still unclear. A dependence of the permeation parameters on the direction of the monoterpene transport could not be observed. Moreover, there are some indications that, in spite of its heterogeneous character, the cuticular membrane of Citrus is homogeneous in respect to the transport of small gaseous molecules. An exposure to environmentally relevant ozone concentrations for 6 months did not change the permeation characteristics of the membrane. Due to the high variability of the samples only a tendency towards higher permeability coefficients of cuticles treated with 80 ppb ozone was observed. This may be attributed to a reduced tension of the membrane caused by chain fractions.