Biochemical and immunohistochemical analysis of pectic polysaccharides in the cell walls of Arabidopsis mutant QUASIMODO 1 suspension-cultured cells: implications for cell adhesion.
Mutation in the Arabidopsis thaliana QUASIMODO 1 gene (QUA1), which encodes a putative glycosyltransferase, reduces cell wall pectin content and cell adhesion. Suspension-cultured calli were generated from roots of wild-type (wt) and qua1-1 A. thaliana plants. The altered cell adhesion phenotype of the qua1-1 plant was also found with its suspension-cultured calli. Cell walls of both wt and qua1-1 calli were analysed by chemical, enzymatic and immunohistochemical techniques in order to assess the role of pectic polysaccharides in the mutant phenotype. Compared with the wt, qua1-1 calli cell walls contained more arabinose (23.6 versus 21.6 mol%), rhamnose (3.1 versus 2.7 mol%), and fucose (1.4 versus 1.2 mol%) and less uronic acid (24.2 versus 27.6 mol%), and they were less methyl-esterified (DM: 22.9% versus 30.3%). When sequential pectin extraction of calli cell walls was performed, qua1-1 water-soluble and chelator-soluble extracts contained more arabinose and less uronic acid than wt. Water-soluble pectins were less methyl-esterified in qua1-1 than in wt. Chelator-soluble pectins were more acetyl-esterified in qua1-1. Differences in the cell wall chemistry of wt and mutant calli were supported by a reduction in JIM7 labelling (methyl-esterified homogalacturonan) of the whole wall in small cells and particularly by a reduced labelling with 2F4 (calcium-associated homogalacturonan) in the middle lamella at tricellular junctions of large qua1-1 cells. Differences in the oligosaccharide profile obtained after endopolygalacturonase degradation of alkali extracts from qua1-1 and wt calli indicated variations in the structure of covalently bonded homogalacturonan. About 29% more extracellular polymers rich in pectins were recovered from the calli culture medium of qua1-1 compared with wt. These results show that perturbation of QUASIMODO 1-1 gene expression in calli resulted in alterations of homogalacturonan content and cell wall location. The consequences of these structural variations are discussed with regard to plant cell adhesion.
Leboeuf
Edouard
E
INRA-Biopolymères, Interactions, Assemblages, BP 71627, F-44316 Nantes Cedex 3, France.
Guillon
Fabienne
F
Thoiron
Séverine
S
Lahaye
Marc
M
D000468:Alkalies; D017360:Arabidopsis / Q000737:chemistry* / Q000166:cytology / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics*; D002118:Calcium / Q000032:analysis; D002448:Cell Adhesion; D002473:Cell Wall / Q000737:chemistry / Q000648:ultrastructure; D002478:Cells, Cultured; D002614:Chelating Agents; D003470:Culture Media / Q000737:chemistry; D007150:Immunohistochemistry; D007365:Intercellular Junctions / Q000737:chemistry; D009154:Mutation; D010368:Pectins / Q000032:analysis* / Q000737:chemistry*; D011134:Polysaccharides / Q000032:analysis
D000468:Alkalies; D029681:Arabidopsis Proteins; D002614:Chelating Agents; D003470:Culture Media; D011134:Polysaccharides; D010368:Pectins; D002118:Calcium; C003181:polygalacturonic acid