Inhibition of auxin‐induced elongation and xyloglucan breakdown in azuki bean epicotyl segments by fucose‐binding lectins

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Abstract
Auxin‐induced elongation of epicotyl segments of azuki bean (Vigna angularis Ohwi and Ohashi cv. Takara) was suppressed by fucose‐binding lectins from Tetragonolobus purpureus Moench and Ulex europaeus L. These lectins also inhibited auxin‐induced cell wall loosening (decrease in the minimum stress‐relaxation time of the cell walls) of segments. Auxin caused a decrease in molecular mass of xyloglucans extracted with 24% KOH from the cell walls. The lectins inhibited auxin‐induced changes in molecular mass of the xyloglucans. The autolytic release of xylose‐containing products from the pectinase‐treated cell walls was also suppressed by the lectins. Fucose‐binding lectins pretreated with fucose exhibited little or no inhibitory effect on auxin‐induced elongation, cell wall loosning, or breakdown of xyloglucans. These results support the view that the breakdown of xyloglucans is involved in the cell wall loosening responsible for auxin‐induced elongation in dicotyledons.