DEVELOPMENTAL AND TISSUE-SPECIFIC STRUCTURAL ALTERATIONS OF THE CELL-WALL POLYSACCHARIDES OF ARABIDOPSIS-THALIANA ROOTS

The plant cell wall is a dynamic structure that plays important roles in growth and development and in the interactions of plants with their environment and other organisms. We have used monoclonal antibodies t hat recognize different carbohydrate epitopes present in plant cell-wa ll polysaccharides to locate these epitopes in roots of developing Ara bidopsis thaliana seedlings. An epitope in the pectic polysaccharide r hamnogalacturonan I is observed in the walls of epidermal and cortical cells in mature parts of the root. This epitope is inserted into the walls in a developmentally regulated manner. Initially, the epitope is observed in atrichoblasts and later appears in trichoblasts and simul taneously in cortical cells. A terminal alpha-fucosyl-containing epito pe is present in almost all of the cell walls in the root. An arabinos ylated (1-->6)-beta-galactan epitope is also found in all of the cell walls of the root with the exception of lateral root-cap cell walls. I t is striking that these three polysaccharide epitopes are not uniform ly distributed (or accessible) within the walls of a given cell, nor a re these epitopes distributed equally across the two walls laid down b y adjacent cells. Our results further suggest that the biosynthesis an d differentiation of primary cell walls in plants are precisely regula ted in a temporal, spatial, and developmental manner.