title: Ultradian rhythms in Arabidopsis thaliana leaves in microgravity.
abstract: Ultradian movements of Arabidopsis thaliana rosette leaves were discovered and studied under microgravity conditions in space. Weightlessness revealed new facets of these movements. The European Modular Cultivation System (EMCS) was used in a long-term white-light, light-darkness (LD; 16 : 8 h) experiment on the International Space Station (ISS). Leaves reacted with slow up or down movement (time constant several hours) after transitions to darkness or light, respectively. Superimposed movements with periods of c. 80-90 min and small-amplitude pulsed movements of 45 min were present in the light. Signal analysis (fast Fourier transform (FFT) analysis) revealed several types and frequencies of movements. Identical phase coupling was observed between the 45-min movements of the leaves of one plant. In darkness, movements of c. 120-min period were recorded. The EMCS allowed 0-g to 1-g transitions to be created. Leaves on plants germinated in microgravity started a negative gravitropic reaction after a delay of c. 30 min. Leaves grown on a 1-g centrifuge reacted to the same transition with an equal delay but had a weaker gravitropic response. The experiments provide unequivocal demonstrations of ultradian, self-sustained rhythmic movements in A. thaliana rosette leaves in the absence of the effect of gravity.
authors.affiliation: Department of Physics, Norwegian University of Science and Technology, N-7491 Trondheim, Norway.
authors.forename: B G B
authors.initials: BGB
authors.lastname: Solheim
authors.affiliation: Department of Physics, Norwegian University of Science and Technology, N-7491 Trondheim, Norway.
authors.forename: A
authors.initials: A
authors.lastname: Johnsson
authors.affiliation: Department of Biology, The Plant BioCentre, Norwegian University of Science and Technology, N-7491 Trondheim, Norway.
authors.forename: T-H
authors.initials: TH
authors.lastname: Iversen
mesh_terms: D017360:Arabidopsis / Q000502:physiology*; D002498:Centrifugation; D003624:Darkness; D018522:Gravitropism; D008027:Light; D009068:Movement; D010507:Periodicity; D018515:Plant Leaves / Q000502:physiology*; D013026:Space Flight; D013997:Time Factors; D014893:Weightlessness