Abstract
The role of the cortical microtubule (cMT) orientation during gravitropism was studied in azuki bean epicotyl. When a seedling was placed horizontally, the epicotyl bent upward. Cells with longitudinal cMT increased in upper epidermis, and those with transverse cMT did in lower epidermis. When epicotyls were mechanically kept straight during gravi-stimulation, no change of cMT orientation occurred. When an epicotyl was enforced to bend downward, cells with transverse cMT increased in upper epidermis, and those with longitudinal cMT did in lower epidermis. When epicotyls were loaded with NPA, an inhibitor of auxin transport, both gravitropic bending and change of cMT orientation were inhibited. However, change of cMT orientation was induced by enforced bending. The cMT orientation seems to be controlled by the bending of epicotyl. Gd3+, inhibited cMT reorientation, suggesting involvement of stretch-activated ion channel.
