Hypergravity increases the molecular mass of xyloglucans by decreasing xyloglucan-degrading activity in azuki bean epicotyls

Elongation growth of dark-grown azuki bean (Vigna angularis Ohwi et Ohashi cv. Takara) epicotyls was suppressed by hypergravity at 30 x g and above. A cceleration at 300 x g significantly decreased the mechanical extensibility of cell walls. The amounts of cell mall polysaccharides (pectin, hemicellu lose-II and cellulose) per unit length of epicotyls increased under the hyp ergravity condition. Hypergravity also increased the amounts and the weight -average molecular mass of xyloglucans in the hemicellulose-II fraction, wh ile decreasing the activity of xyloglucan-degrading enzymes extracted from epicotyl cell malls. These results suggest that hypergravity increases the amounts and the molecular mass of xyloglucans by decreasing xyloglucan-degr ading activity. Modification of xyloglucan metabolism as well as the thicke ning of cell walls under hypergravity conditions seems to be involved in ma king the cell mall mechanically rigid, thereby inhibiting elongation growth of azuki bean epicotyls.