THE COMPOSITION AND PHYLOGENETIC SIGNIFICANCE OF THE MOUGEOTIA (CHAROPHYCEAE) CELL WALL

The two-layered, fibrillar cell wall of Mougeotia C. Agardh sp. consisted of 63.6% non-cellulosic carbohydrates and 13.4% cellulose. The orientation of cellulose microfibrils in the native cell wall agrees with the multinet growth hypothesis, which has been employed to explain the shift in microfibril orientation from transverse (inner-wall) toward axial (outer wall). Monosaccharide analysis of isolated cell walls revealed the presence of ten sugars with glucose, xylose and galactose most abundant. Methylation analysis of the acid-modified, 1 N NaOH insoluble residue fraction showed that it was composed almost exclusively of 4-linked glucose, confirming the presence of cellulose. Mougeotia cell wall composition is similar to that of Klebsormidium (Charophyceae) and has homologies with vascular plant cell walls. Our observations support ultrastructural evidence which suggests that members of the Charophyceae represent the phylogenetic line that gave rise to vascular plants. Therefore, the primary cell walls of vascular plants may have evolved directly from structures typical of the filamentous green algal cell walls found in the Charophyceae.