Temporal and spatial regulation of pectic (1 -> 4)-beta-D-galactan in cellwalls 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. Monoclon al antibodies to epitopes occurring in homo- galacturonan and side chains o f rhamnogalacturonan I have been used in an immunolocalization study of cel l wall architecture of developing pea cotyledons. Pectic (1 --> 4)-beta-d-g alactan appears in cotyledon cell walls at a defined stage late in developm ent (approximately 26-30 days after anthesis), whereas homogalacturonan and pectic (1 --> 5)-alpha-L-arabinan are present in cotyledon cell walls thro ughout development. (1 --> 4)-beta-galactan was restricted to a distinct th in layer at the plasma membrane face of the cell wall. Anion exchange and i mmunoaffinity chromatography indicated that the (1 --> 4)-beta-galactan was associated with acidic pectic components. Mechanical compressive testing o f pea cotyledons, before and after (1 --> 4)-beta-galactan appearance, indi cated that the cotyledons with the galactan-rich cell wall layer were twice as firm as those with no detectable (1 --> 4)-beta-galactan.