Water sorption-desorption in conifer cuticles: The role of lignin

Current information on the type and amount of biopolymers present in the ep idermis of conifer species is still insufficient. This work presents the de tailed morphology and chemical composition of Araucaria bidwillii cuticle a fter selective treatments to remove the different types of biopolymers. Aft er removal of the waxes, cutin and polar hydrolyzable components, a lignin- like fraction, which makes up 25% of the initial cuticle weight, was identi fied by GC-MS and infrared spectroscopy. The isolated lignin is of G type, mainly formed by guaiacyl units, This composition indicates that the conife r cuticle investigated here has similar composition to of her conifer-isola ted cuticles, Wafer sorption and desorption by the isolated cuticle and the different cuticle fractions, including lignin, were studied. The analysis of the isotherms, following distinct physicochemical models, gave useful in formation on tbe structural and physiological role of the different biopoly mers present in the cuticle. Lignin fraction showed both a high water sorpt ion and capability of retaining it in comparision to other cuticle componen ts. Hysteresis effect on water sorption-desorption cycle and water cluster formations has also been studied, and their physiological role discussed.