Metabolic Regulation of the Gene Encoding Glutamine-Dependent Asparagine Synthetase in Arabidopsis thaliana

Abstract

We have characterized the gravitropic response of inflorescence stems in Arabidopsis thaliana. When the inflorescence stems were placed horizontally, they curved upward about 90[deg] within 90 min in darkness at 23[deg]C, exhibiting strong negative gravitropism. Decapitated stem segments (without all flowers, flower buds, and apical apices) also showed gravitropic responses when they included the elongation zone. This result indicates that the minimum elements needed for the gravitropic response exist in the decapitated inflorescence stem segments. At least the 3-min gravistimulation time was sufficient to induce the initial curvature at 23[deg]C after a lag time of about 30 min. In the gravitropic response of inflorescence stems, (a) the gravity perception site exists through the elongating zone, (b) auxin is involved in this response, (c) the gravitropic curvature was inhibited at 4[deg]C but at least the gravity perception step could occur, and (d) two curvatures could be induced in sequence at 23[deg]C by two opposite directional horizontal gravistimulations at 4[deg]C.