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

Cuticular waxes from grape berry cuticle of Vitis vinifera L. have been inv estigated by X-ray diffraction, differential scanning calorimetry and gas c hromatography. The waxes were mainly composed of n-alcohols and n-fatty aci ds and a considerable amount (about 30%) of the cyclic terpenoid oleanolic acid. The physical techniques used showed that the waxes have a high degree of molecular order in spite of the presence of the cyclic component, Molec ular dynamics of the reconstituted waxes were measured to characterize the transport properties of the cuticular waxes that form the transport-limitin g barrier of plant cuticles. For this purpose, the diffusion coefficient of labelled cholesterol, imitating the terpenoic acid, was measured. The valu e obtained was around 10(-21) m(2) s(-1) indicating a low mobility of the c yclic part of the reconstituted waxes. Temperature dependence of the diffus ion coefficient was studied in the range of 5-45 degrees C. Arrhenius plot analysis yielded a high activation energy, 196.4 kJ mol(-1), of the diffusi on process. This indicates dense molecular packing of reconstituted cuticul ar waxes.