Parenchyma cell wall structure in twining stem of Dioscorea balcanica

Abstract

Anatomical adaptation of liana plants includes structural changes in cell walls of different tissues: fibers, vessel elements and tracheids. However, the contribution of parenchyma cells to stem twining in liana plants is mostly unknown. The aim of this investigation is to determine changes in stem parenchyma cell walls that are correlated with the twinning process in liana plants. Parenchyma cell wall structure was studied on the stem cross sections of straight and twisted internodes of monocotyledonous liana Dioscorea balcanica, by different microscopy techniques: light microscopy, scanning electron microscopy, fluorescence detected linear dichroism microscopy and Fourier transform infrared microspectrometry. In addition, chemical analysis of the entire stem internodes was performed using photometric and chromatographic methods. Parenchyma cell walls of twisted D. balcanica internodes are characterized by: lower amounts of cellulose (obtained by FTIR microspectrometry) with different cellulose microfibril orientation (shown by Scanning electron microscopy), but no changes in "cellulose fibril order" (obtained by Differential polarization laser scanning microscopy); lower amounts of xyloglucan, higher amounts of xylan, higher amounts of lignin with modified organization-less condensed lignin (obtained by FTIR microspectrometry). At the same time, chemical analysis of the entire internodes did not show significant differences in lignin content and cell wall bound phenols related to stem twining, except for the presence of diferulate cross-links exclusively in twisted internodes. Our results indicate that adaptations to mechanical strain in D. balcanica stems involve modifications in parenchyma cell wall structure and chemistry, which provide decreased stiffness, higher strength and increased elasticity of twisted internodes.