Anatomy and Lignin Characterisation of Twigs in the Chaparral Shrub Rhamnus Californica

Abstract

Characterisation of anatomical properties and analysis of lignin content and monomer composition were performed on twigs of the shrub Rhamnus californica L. in order to highlight their role in the adaptive strategies of this species in Mediterranean-type ecosystems. Our results showed that R. californica twigs develop a thick cuticle accompanied by several layers of subepidermal cells with suberised walls aiming to save water. The xylem is characterised by anatomical and chemical traits ensuring safety of water transport and preventing permanent damage through the enhancement of mechanical strength, also favoured by the lignification of pith cell walls. Moreover, the accumulation of phenolic compounds in the cortical cylinder is a strategy to protect against herbivory and to screen against high levels of radiation. Our overall analysis suggests that R. californica has evolved a strategy of shoot development that allows it to cope with the multiple environmental stresses found in Mediterraneantype ecosystems, among which summer drought and grazing play a major role especially for the survival of seedlings and young plants.