2011 年 55 巻 3 号 p. 113-117
Stem segments excised from vegetatively growing shoots of floating rice displayed a gravitropic curvature in response to gravistimulation. Using stem segments, we investigated the involvement of plant hormones in the gravitropic bending response of pulvini and the effect of submergence on the response. The application of the auxin transport inhibitor N-1-naphthylphthalamic acid to gravistimulated stem segments resulted in a 75% reduction in the bending of the pulvini, which was completely removed by unilateral application of indole-3-acetic acid to the underside of the pulvini. Although the exclusive application of gibberellic acid (GA3) did not affect the bending response of gravistimulated pulvini, the gibberellin biosynthesis inhibitor ancymidol reduced the bending of gravistimulated pulvini by 30%, and the reduction was removed by the application of GA3. In addition, the application of ethylene alone did not affect the bending response of gravistimulated pulvini, although gravistimulation promoted the production of ethylene in stem segments. The ethylene biosynthesis inhibitor aminooxyacetic acid suppressed the bending response of gravistimulated pulvini by 28%, and the suppression was removed by the application of ethylene. These results suggest that the asymmetric distribution of auxin in gravistimulated tissues of floating rice pulvini plays an important role in the bending response, in which gibberellins and ethylene might also be, at least, partly involved. The gravitropic bending of floating rice stem segments occurred under submergence under both light and dark conditions, whereas the gravitropic bending of submerged stem segments of wheat and oat was still observed under light but not under dark conditions.
