A xylogalacturonan epitope is specifically associated with plant cell detachment.

A monoclonal antibody (LM8) was generated with specificity for xyloglacturonan (XGA) isolated from pea (Pisum sativum L.) testae. Characterization of the LM8 epitope indicates that it is a region of XGA that is highly substituted with xylose. Immunocytochemical analysis indicates that this epitope is restricted to loosely attached inner parenchyma cells at the inner face of the pea testa and does not occur in other cells of the testa. Elsewhere in the pea seedling, the LM8 epitope was found only in association with root cap cell development at the root apex. Furthermore, the LM8 epitope is specifically associated with root cap cells in a range of angiosperm species. In embryogenic carrot suspension cell cultures the epitope is abundant at the surface of cell walls of loosely attached cells in both induced and non-induced cultures. The LM8 epitope is the first cell wall epitope to be identified that is specifically associated with a plant cell separation process that results in complete cell detachment.

Altered cell wall disassembly during ripening of Cnr tomato fruit: implications for cell adhesion and fruit softening.

The Cnr ( C olourless n on- r ipening) tomato ( Lycopersicon esculentum Mill.) mutant has an aberrant fruit-ripening phenotype in which fruit do not soften and have reduced cell adhesion between pericarp cells. Cell walls from Cnr fruit were analysed in order to assess the possible contribution of pectic polysaccharides to the non-softening and altered cell adhesion phenotype. Cell wall material (CWM) and solubilised fractions of mature green and red ripe fruit were analysed by chemical, enzymatic and immunochemical techniques. No major differences in CWM sugar composition were detected although differences were found in the solubility and composition of the pectic polysaccharides extracted from the CWM at both stages of development. In comparison with the wild type, the ripening-associated solubilisation of homogalacturonan-rich pectic polysaccharides was reduced in Cnr. The proportion of carbohydrate that was chelator-soluble was 50% less in Cnr cell walls at both the mature green and red ripe stages. Chelator-soluble material from ripe-stage Cnr was more susceptible to endo-polygalacturonase degradation than the corresponding material from wild-type fruit. In addition, cell walls from Cnr fruit contained larger amounts of galactosyl- and arabinosyl-containing polysaccharides that were tightly bound in the cell wall and could only be extracted with 4 M KOH, or remained in the insoluble residue. The complexity of the cell wall alterations that occur during fruit ripening and the significance of different extractable polymer pools from cell walls are discussed in relation to the Cnr phenotype.