title: Gravity amplifies and microgravity decreases circumnutations in Arabidopsis thaliana stems: results from a space experiment.
abstract: In a microgravity experiment onboard the International Space Station, circumnutations of Arabidopsis thaliana were studied. Plants were cultivated on rotors under a light:dark (LD) cycle of 16 : 8 h, and it was possible to apply controlled centrifugation pulses. Time-lapse images of inflorescence stems (primary, primary axillary and lateral inflorescences) documented the effect of microgravity on the circumnutations. Self-sustained circumnutations of side stems were present in microgravity but amplitudes were mostly very small. In darkness, centrifugation at 0.8 g increased the amplitude by a factor of five to ten. The period at 0.8 g was c. 85 min, in microgravity roughly of the same magnitude. In white light the period decreased to c. 60 min at 0.8 g (microgravity value not measurable). Three-dimensional data showed that under 0.8 g side stems rotated in both clockwise and counter-clockwise directions. Circumnutation data for the main stem in light showed a doubling of the amplitude and a longer period at 0.8 g than in microgravity (c. 80 vs 60 min). For the first time, the importance of gravity in amplifying minute oscillatory movements in microgravity into high-amplitude circumnutations was unequivocally demonstrated. The importance of these findings for the modelling of gravity effects on self-sustained oscillatory movements is discussed.
authors.affiliation: Department of Physics, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway.
authors.forename: A
authors.initials: A
authors.lastname: Johnsson
authors.affiliation: Department of Physics, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway.
authors.forename: B G B
authors.initials: BGB
authors.lastname: Solheim
authors.affiliation: Department of Biology, The Plant BioCentre, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
authors.forename: T-H
authors.initials: TH
authors.lastname: Iversen