124. Hotchkiss, Jr. A. T., Gretz, M. R.,
Hicks, K. B., and R. M. Brown, Jr. 1989. The composition and phylogenetic
significance of the Mougeotia (Charophyceae) cell wall.
Journal of Phycology.25:646-654.
124. Abstract
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. The major cellulosic carbohydrate was semi-purified
by DEAE Sephacel (Cl-) anion-exchange chromatography of the hot
1 N NaOH soluble fraction. This hemicellulose was a xylan consisting
of a 4-xylosyl backbone and 2,4-xylosyl branchpoints. The major
hot water soluble neutral polysaccharide was identified as a 3-linked
galactan. 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.