Structure and dynamics of reconstituted cuticular waxes of grape berry cuticle (Vitis vinifera L.)

Cuticular waxes from grape berry cuticle of Vitisvinifera L. have been investigated by X-ray diffraction,differential scanning calorimetry and gas chromatography. The waxes weremainly composed of n-alcohols andn-fatty acids and a considerable amount (about 30%) ofthe cyclic terpenoid oleanolic acid. The physical techniques used showedthat the waxes have a high degree of molecular order in spite of thepresence of the cyclic component. Molecular dynamics of the reconstitutedwaxes were measured to characterize the transport properties of thecuticular waxes that form the transport-limiting barrier of plant cuticles.For this purpose, the diffusion coefficient of labelled cholesterol,imitating the terpenoic acid, was measured. The value obtained was around10^-21 m²s^-1 indicating a low mobility of the cyclic part ofthe reconstituted waxes. Temperature dependence of the diffusioncoefficient was studied in the range of 5-45C. Arrhenius plot analysis yielded a high activationenergy, 196.4 kJ mol^-1, of the diffusion process.This indicates dense molecular packing of reconstituted cuticularwaxes.