title: Effect of chilling on the gravitropic response of 'Poinsett 76' cucumber (Cucumis sativus L.) radicles.
abstract: Germinating 'Poinsett 76' cucumber (Cucumis sativus) seeds are chilling sensitive, and subsequent radicle elongation is inhibited by exposure to nonfreezing temperatures below 10 degrees C. Reorienting germinated seeds with 5-mm-long radicles from a vertical to a horizontal position induced gravitropic curvature within 2 hours at 10 to 25 degrees C without significantly affecting the rate of radicle elongation. However, neither elongation nor curvature occurred in similar seeds held at 2.5 or 5 degrees C. Chilling seeds with 5-mm-long radicles at 2.5 degrees C for 18 hours significantly reduced the subsequent rate of radicle elongation at 25 degrees C by 47% compared with nonchilled control, while gravitropic curvature was reduced by only 34%. After 36 hours of recovery at 25 degrees C, the difference was even more pronounced; elongation was reduced by 26% while curvature was reduced by only 6%. Clearly, gravitropic curvature was less chilling sensitive than radicle elongation, despite the fact that differential elongation of cells in the radicle are needed to produce curvature. Exposing seeds with 5-mm-long radicles to a heat shock of 45 degrees C for 4 to 10 minutes significantly diminished the chilling-induced reduction in radicle elongation and gravitropic curvature.
authors.affiliation: Department of Vegetable Crops, University of California, Davis 95616-8631, USA.
authors.forename: A
authors.initials: A
authors.lastname: Rab
authors.forename: M E
authors.initials: ME
authors.lastname: Saltveit
mesh_terms: D003080:Cold Temperature / Q000009:adverse effects*; D018553:Cucumis sativus / Q000196:embryology / Q000254:growth & development*; D006112:Gravitation; D018522:Gravitropism / Q000502:physiology*; D018517:Plant Roots / Q000254:growth & development*; D012639:Seeds / Q000254:growth & development*; D013997:Time Factors