Lignin distribution in the tropical bamboo species Gigantochloa levis

Abstract

The lignin distribution within the cell walls of Gigantochloa levis was studied topochemically by means of TEM and cellular UV microspectrophotometry. The distribution of lignin structural units in different anatomical regions is described and lignification of the tropical bamboo species Gigantochloa levis is compared with that of the temperate bamboo species Phyllostachys viridiglaucescens. Considerable differences were found in cell wall structure between fibres adjacent to the vascular tissue, fibres of free fibre strands and parenchyma cells. The 82 fibre wall in general has a lamellar structure with an increasing lignin content from the centre towards the compound middle lamella. P-coumaric and ferulic acids are more widely distributed in G. levis and their content depends on the anatomical location. The early maturing fibres adjacent to the vascular tissue and at the outer culm wall reveal a maximum absorbance at 280 nm (guaiacyl peak) whereas the late maturing fibres display a shoulder at 310-320 nm. This is in contrast to P. viridiglaucescens where the late maturing fibres also show a maximum peak at 280 nm. The compound middle lamellae show higher absorbance values and are richer p-coumaric and ferulic acid esters in comparison to the S2 wall layers. The vessel walls have a lower lignin content. A difference in lignin content between the various ages and between flowering and non-flowering culms could not be observed.