Abstract
We examined the changes in the orientation of cortical microtubules and the expression of γ-tubulin gene during the hypergravity-induced modification of growth anisotropy (inhibition of elongation growth and promotion of lateral growth) in azuki bean epicotyls. Hypergravity caused a reorientation of cortical microtubules from transverse to longitudinal directions. By removal of hypergravity stimulus, the orientation of microtubules changed from longitudinal to transverse directions. Hypergravity increased the expression of γ-tubulin gene transiently. Also, the expression of γ-tubulin gene was increased transiently by removal of hypergravity stimulus. Lanthanum and gadolinium, blockers of calcium channels, nullified the modification of growth anisotropy, reorientation of microtubules, and up-regulation of γ-tubulin gene expression by hypergravity. These results suggest that mechanoreceptors on the plasma membrane may perceive the gravity signal, which leads to reorientation of cortical microtubules by transiently increasing the levels of γ-tubulin, thereby modifying growth anisotropy of azuki bean epicotyls.
