Different Cell Wall Polysaccharides are Responsible for Gravity Resistance in the Upper and the Basal Regions of Azuki Bean Epicotyls

抄録

Effects of hypergravity on growth and the levels of cell wall polysaccharides were examined along epicotyls of dark-grown azuki bean (Vigna angularis Ohwi et Ohashi cv. Erimowase). Elongation growth occurred only in the upper regions, which was suppressed by hypergravity at 300 G. The fresh weight also increased in the upper regions, but hypergravity increased it only slightly in the basal regions. The thickness of epicotyls was increased clearly in the upper regions and slightly in the basal regions by hypergravity. The levels of pectin, hemicellulose-I, and hemicellulose-II per unit length of epicotyl were increased by hypergravity in the upper regions, but not in the basal ones. Also, the levels of xyloglucans were increased by hypergravity only in the upper regions. On the other hand, the levels of cellulose per unit length increased from the apical to the basal regions, and hypergravity further increased the levels in all regions. These results suggest that cellulose, instead of xyloglucans, acts as anti-gravitational polysaccharides in the basal regions. Cellulose and xyloglucans may cooperate in resistance of whole stem organs to the gravitational force.