title: Sugar composition of the pectic polysaccharides of charophytes, the closest algal relatives of land-plants: presence of 3-O-methyl-D-galactose residues.
abstract: OBJECTIVE
  During evolution, plants have acquired and/or lost diverse sugar residues as cell-wall constituents. Of particular interest are primordial cell-wall features that existed, and in some cases abruptly changed, during the momentous step whereby land-plants arose from charophytic algal ancestors.
  
  
  METHODS
  Polysaccharides were extracted from four charophyte orders [Chlorokybales (Chlorokybus atmophyticus), Klebsormidiales (Klebsormidium fluitans, K. subtile), Charales (Chara vulgaris, Nitella flexilis), Coleochaetales (Coleochaete scutata)] and an early-diverging land-plant (Anthoceros agrestis). 'Pectins' and 'hemicelluloses', operationally defined as extractable in oxalate (100 °C) and 6 m NaOH (37 °C), respectively, were acid- or Driselase-hydrolysed, and the monosaccharides analysed chromatographically. One unusual monosaccharide, 'U', was characterized by (1)H/(13)C-nuclear magnetic resonance spectroscopy and also enzymically.
  
  
  RESULTS
  'U' was identified as 3-O-methyl-D-galactose (3-MeGal). All pectins, except in Klebsormidium, contained acid- and Driselase-releasable galacturonate, suggesting homogalacturonan. All pectins, without exception, released rhamnose and galactose on acid hydrolysis; however, only in 'higher' charophytes (Charales, Coleochaetales) and Anthoceros were these sugars also efficiently released by Driselase, suggesting rhamnogalacturonan-I. Pectins of 'higher' charophytes, especially Chara, contained little arabinose, instead possessing 3-MeGal. Anthoceros hemicelluloses were rich in glucose, xylose, galactose and arabinose (suggesting xyloglucan and arabinoxylan), none of which was consistently present in charophyte hemicelluloses.
  
  
  CONCLUSIONS
  Homogalacturonan is an ancient streptophyte feature, albeit secondarily lost in Klebsormidium. When conquering the land, the first embryophytes already possessed rhamnogalacturonan-I. In contrast, charophyte and land-plant hemicelluloses differ substantially, indicating major changes during terrestrialization. The presence of 3-MeGal in charophytes and lycophytes but not in the 'intervening' bryophytes confirms that cell-wall chemistry changed drastically between major phylogenetic grades.
authors.affiliation: The Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, The University of Edinburgh, Daniel Rutherford Building, The King's Buildings, Max Born Crescent, Edinburgh EH9 3BF, UK and.
authors.forename: Christina
authors.initials: C
authors.lastname: O'Rourke
authors.affiliation: The Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, The University of Edinburgh, Daniel Rutherford Building, The King's Buildings, Max Born Crescent, Edinburgh EH9 3BF, UK and.
authors.forename: Timothy
authors.initials: T
authors.lastname: Gregson
authors.affiliation: EastChem School of Chemistry, The University of Edinburgh, The King's Buildings, Edinburgh EH9 3JJ, UK.
authors.forename: Lorna
authors.initials: L
authors.lastname: Murray
authors.affiliation: EastChem School of Chemistry, The University of Edinburgh, The King's Buildings, Edinburgh EH9 3JJ, UK.
authors.forename: Ian H
authors.initials: IH
authors.lastname: Sadler
authors.affiliation: The Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, The University of Edinburgh, Daniel Rutherford Building, The King's Buildings, Max Born Crescent, Edinburgh EH9 3BF, UK and s.fry@ed.ac.uk.
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Fry
mesh_terms: D002458:Cell Fractionation; D002473:Cell Wall / Q000737:chemistry; D057946:Charophyceae / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D002854:Chromatography, Paper; D002855:Chromatography, Thin Layer; D019669:Embryophyta / Q000737:chemistry*; D005656:Fungal Proteins / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000378:metabolism; D008756:Methylgalactosides / Q000032:analysis*; D009005:Monosaccharides / Q000032:analysis; D010368:Pectins / Q000032:analysis*; D011134:Polysaccharides / Q000032:analysis*; D066244:Proton Magnetic Resonance Spectroscopy; D012015:Reference Standards; D013237:Stereoisomerism
chemical_list: D005656:Fungal Proteins; D008756:Methylgalactosides; D009005:Monosaccharides; D011134:Polysaccharides; C031552:methyl beta-galactoside; C007916:hemicellulose; D010368:Pectins; D006026:Glycoside Hydrolases; C035212:driselase
keywords: 3-O-methyl-d-galactose; Chara; Charophytic algae; Chlorokybus; Coleochaete; Embryophyta; Klebsormidium; Streptophyta; charophytes; pectic polysaccharides; pectin; plant cell-wall evolution; rhamnogalacturonan-I