Distribution of lignin in vascular bundles of coconut wood (Cocos nucifera) by cellular UV-spectroscopy and relationship between lignification and tensile strength in single vascular bundles

Abstract

Abstract The topochemical distribution of lignin in vascular bundles separated from different radial positions of Mexican coconut wood stems (Cocos nucifera) has been studied with focus on the relationship between the degree of lignification and tensile strength properties. The cellular lignin distribution was analyzed by UV-microspectrophotometry (UMSP) scanning at 280 nm of sections of vascular bundles (VBs) of 1 μm thickness. The fibers of the VBs with high tensile strength reveal a relatively low UV-absorbance at 280 nm (A280 nm 0.39), whereas the VBs with low tensile strength display the highest A280 nm (0.59). The S2 of fiber walls are characterized by the typical lamellar structure with increasing lignin contents from the cell lumen towards the compound middle lamellae (CML). The A280 nm data of CMLs are higher (0.67 to 0.87) than those of the S2 wall layers. Overall, the A280 nm values of S2 of fibers walls within single VBs of coconut are in the range of 0.36 to 0.59.