title: Analyses of a gravistimulation-specific Ca2+ signature in Arabidopsis using parabolic flights.
abstract: Gravity is a critical environmental factor affecting the morphology and functions of organisms on the Earth. Plants sense changes in the gravity vector (gravistimulation) and regulate their growth direction accordingly. In Arabidopsis (Arabidopsis thaliana) seedlings, gravistimulation, achieved by rotating the specimens under the ambient 1g of the Earth, is known to induce a biphasic (transient and sustained) increase in cytoplasmic calcium concentration ([Ca(2+)]c). However, the [Ca(2+)]c increase genuinely caused by gravistimulation has not been identified because gravistimulation is generally accompanied by rotation of specimens on the ground (1g), adding an additional mechanical signal to the treatment. Here, we demonstrate a gravistimulation-specific Ca(2+) response in Arabidopsis seedlings by separating rotation from gravistimulation by using the microgravity (less than 10(-4)g) conditions provided by parabolic flights. Gravistimulation without rotating the specimen caused a sustained [Ca(2+)]c increase, which corresponds closely to the second sustained [Ca(2+)]c increase observed in ground experiments. The [Ca(2+)]c increases were analyzed under a variety of gravity intensities (e.g. 0.5g, 1.5g, or 2g) combined with rapid switching between hypergravity and microgravity, demonstrating that Arabidopsis seedlings possess a very rapid gravity-sensing mechanism linearly transducing a wide range of gravitational changes (0.5g-2g) into Ca(2+) signals on a subsecond time scale.
authors.affiliation: Department of Physiology, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan.
authors.forename: Masatsugu
authors.initials: M
authors.lastname: Toyota
authors.forename: Takuya
authors.initials: T
authors.lastname: Furuichi
authors.forename: Masahiro
authors.initials: M
authors.lastname: Sokabe
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tatsumi
mesh_terms: D000054:Acceleration; D000401:Aircraft; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006112:Gravitation; D006813:Humidity; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007700:Kinetics; D011312:Pressure; D012399:Rotation; D036226:Seedlings / Q000187:drug effects / Q000502:physiology; D013696:Temperature; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D015544:Inositol 1,4,5-Trisphosphate; D010738:Type C Phospholipases; D002118:Calcium