COMPOSITION AND LOCALIZATION OF PECTIC POLYMERS IN THE STEMS OF 2 SOLANUM-TUBEROSUM GENOTYPES

Some properties of the cell walls of the stems of two subspecies of So lanum tuberosum, S. t. tuberosum (cv. Bintje) and S.t. andigena (ADG 8 8S-262-7 genotype), selected for their different susceptibility to sof t-rot were investigated by biochemical and immunocytochemical analyses . A greater amount of cell walls could be isolated from the stems of S . t. andigena and this genotype exhibited a lower cell wall exchange c apacity related to a lower amount of calcium content. Pectic fractions analyses revealed that the amount of unesterified uronic acids was lo wer in S. t. andigena. These results pointed out that S. a. andigena h ad some characteristics of a juvenile plant. The differences between t hese genotypes were not corroborated by the immunocytochemical investi gations performed with two monoclonal antibodies, JIM 7 and JIM 5, whi ch recognize highly esterified and poorly esterified epitopes, respect ively. Nevertheless, the cytochemical results provided new information s on pectin distribution in potato stem tissues. With both antibodies, a preferential localization was observed in epidermal cell walls. In cortical parenchyma, poorly esterified epitopes were restricted to the middle lamella and the three-way junctions whereas highly esterified epitopes were evenly distributed throughout the wall. The absence of l abelling over the recently deposited part of the wall pointed out that a demethylation of the newly synthesized polymers might take place wi thin the apoplastic area. The results indicated the occurrence of micr odomains that might influence the susceptibility of the plants to depo lymerizing enzymes of plant pathogens.