Modifications of xyloglucan metabolism in azuki bean epicotyls under hypergravity conditions

We examined the effects of hypergravity on both the synthesis and the depolymerization processes of xyloglucan metabolisms. Azuki bean cuttings were incubated with [6-3H]-l-fucose, and the levels and the molecular size of synthesized xyloglucans were investigated in the upper growing regions of epicotyls. The amounts of radioactivity incorporated into xyloglucan fraction increased during incubation, irrespective of the gravity conditions. 3H-Xyloglucans were eluted in the higher molecular mass regions than xyloglucans already present in the cell wall. Hypergravity at 300 g did not influence the molecular size of newly deposited xyloglucans. Thus, the process of xyloglucan synthesis was not modified by the gravitational force. On the other hand, 3H-xyloglucans obtained from epicotyls grown at 1 g were shifted to the low molecular mass regions during the incubation period, which was inhibited by hypergravity. These results indicate that xyloglucans were deposited into the cell wall as large molecules but they were then depolymerized in the cell wall, and that the inhibition of the depolymerization is mainly responsible for the increase in the molecular size of xyloglucans under hypergravity conditions.