Increased Molecular Mass of Hemicellulosic Polysaccharides is Involved in Growth Inhibition of Maize Coleoptiles and Mesocotyls under Hypergravity Conditions

Zea

mays L. cv. Cross Bantam T51) coleoptiles and mesocotyls was suppressed by hypergravity at 30 g and above. Acceleration at 300 g significantly decreased the mechanical extensibility of cell walls of both organs. Hypergravity increased the amounts of hemicellulose and cellulose per unit length in mesocotyl walls, but not in coleoptile walls. The weight-average molecular masses of hemicellulosic polysaccharides were also increased by hypergravity in both organs. On the other hand, the activities of β-glucanases extracted from coleoptile and mesocotyl cell walls were decreased by hypergravity. These results suggest that the decreased activities of β-glucanases by hypergravity cause an increase in the molecular mass of hemicellulosic polysaccharides of both organs. The upshift of molecular mass of hemicellulosic polysaccharides as well as the thickening of cell walls under hypergravity conditions seems to be involved in making the cell wall mechanically rigid, thereby inhibiting elongation growth of maize coleoptiles and mesocotyls.