Temporal and spatial regulation of pectic (1→4)-β-D-galactan in cell walls of developing pea cotyledons:: implications for mechanical properties

Modifications in cell wall pectic polysaccharides are thought to influence cell-cell adhesion and the mechanical properties of plant tissues. Monoclonal antibodies to epitopes occurring in homo- galacturonan and side chains of rhamnogalacturonan I have been used in an immunolocalization study of cell wall architecture of developing pea cotyledons. Pectic (1 --> 4)-beta-d-galactan appears in cotyledon cell walls at a defined stage late in development (approximately 26-30 days after anthesis), whereas homogalacturonan and pectic (1 --> 5)-alpha-L-arabinan are present in cotyledon cell walls throughout development. (1 --> 4)-beta-galactan was restricted to a distinct thin layer at the plasma membrane face of the cell wall. Anion exchange and immunoaffinity chromatography indicated that the (1 --> 4)-beta-galactan was associated with acidic pectic components. Mechanical compressive testing of pea cotyledons, before and after (1 --> 4)-beta-galactan appearance, indicated that the cotyledons with the galactan-rich cell wall layer were twice as firm as those with no detectable (1 --> 4)-beta-galactan.