Increased molecular mass of hemicellulosic polysaccharides is involved in growth inhibition of maize coleoptiles and mesocotyls under hypergravity conditions

Elongation growth of dark-grown maize (Zea mays L cv. Cross Bantam T51) col eoptiles and mesocotyls was suppressed by hypergravity at 30 g and above. A cceleration at 300 g significantly decreased the mechanical extensibility o f cell walls of both organs. Hypergravity increased the amounts of hemicell ulose and cellulose per unit length in mesocotyl walls, but not in coleopti le walls. The weight-average molecular masses of hemicellulosic polysacchar ides were also increased by hypergravity in both organs. On the other hand, the activities of beta-glucanases extracted from coleoptile and mesocotyl cell walls were decreased by hypergravity. These results suggest that the d ecreased activities of beta-glucanases by hypergravity cause an increase in the molecular mass of hemicellulosic polysaccharides of both organs. The u pshift of molecular mass of hemicellulosic polysaccharides as well as the t hickening of cell walls under hypergravity conditions seems to be involved in making the cell wall mechanically rigid, thereby inhibiting elongation g rowth of maize coleoptiles and mesocotyls.