Effect of lectins on auxin‐induced elongation and wall loosening in oat coleoptile and azuki bean epicotyl segments

Abstract

Auxin‐induced elongation of coleoptile segments of oat (Avena sativa L. cv. Victory) was suppressed by agglutinin from Canavalia ensiformis DC. (concanavalin A), Triticum vulgaris Vill. germ, Dolichos biflorus L., Glycine max Merr. and Limulus polyphemus L. at 0.5 mg ml−1, while that of epicotyl segments of azuki bean (Vigna angularis Ohwi and Ohashi cv. Takara) was suppressed by agglutinin from Canavalia ensiformis DC., Tetragonolobus purpureus Moench and Ulex europaeus L. I when segments were incubated at pH 6.0. These lectins suppressed elongation without any prominent lag period. This suppression of elongation by the lectins was not apparent at pH 4.0. When a ligand for lectins, for instance methyl‐α‐D‐mannopyranoside, was added simultaneously with the lectin, elongation of segments was completely or partly restored. The lectins that suppressed elongation were bound to the cell walls of the segments and inhibited the auxin‐induced cell wall loosening (decrease in the minimum stress‐relaxation time of the cell wall). Thus, the lectins may, at least partly, suppress elongation by inhibiting cell wall loosening. Our results demonstrate that the wall components containing α‐D‐mannose (α‐D‐glucose), N‐acetyl‐D‐glucosamine, N‐acetyl‐D‐galactosamine or D‐glucuronic acid play an important role in wall loosening of oat coleoptiles, while the wall components containing α‐D‐mannose (α‐D‐glucose) or L‐fucose are important for that of azuki epicotyls.