CONCANAVALIN-A INHIBITS AUXIN-INDUCED ELONGATION AND BREAKDOWN OF (1-]3), (1-]4)-BETA-D-GLUCANS IN SEGMENTS OF RICE COLEOPTILES

Concanavalin A (Con A) suppresses auxin-induced elongation of surface-abraded segments from both dicotyledonous and poaceous plants. In coleoptile segments of rice (Oryza saliva L.), the auxin-induced decrease in the minimum stress-relaxation time and increase in the mechanical extensibility of the cell walls were also inhibited by Con A, indicating that the lectin suppresses elongation by inhibiting the cell wall loosening. Auxin caused a decrease in the level of (1 --> 3), (1 --> 4)-beta-D-glucans in the cell walls of rice coleoptile segments, and this decrease was also inhibited by the lectin. Con A suppressed the autolytic hydrolysis of the glucans, as well as their breakdown in vitro by a protein fraction that had been extracted from the cell walls of rice coleoptiles with 1 M NaCl. Furthermore, most of the glucan-hydrolyzing activity of the wall proteins bound to a Con A-Sepharose column, suggesting that glycoprotein enzymes are involved in the hydrolysis. Although Con A also affected the hydrolysis of other wall polysaccharides, the present data, when considered in combination with the inhibitory effects of glucan-specific or glucanase-specific antibodies, support the view that the breakdown of (1 --> 3),(1 --> 4)-beta-D-glucans is associated with the cell wall loosening that is responsible for auxin-induced elongation in Poaceae.