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INDUCTION OF PLANT CURVATURE BY INTRACELLULAR VIBROPHORESIS OF STATOLITHS.   A.A. Kuznetsov¹, O.A. Kuznetsov².   Institute of Biochemical Physics, Russian Acad. Sci., Moscow, Russia, ²Physics Dept., Univ. Missouri, Columbia, 65211.

   Mechanical heterogeneity of statocytes allows stimulation of the gravisensing cells by intracellular displacement of statoliths using forces other than gravity. In a plant subjected to non-symmetric vibrations dense statoliths experience inertial force, which causes their cyclic motion relative to cytoplasm. Given a proper oscillation profile, due to complex rheology of the cell interior, such motion can result in a net statoliths displacement, as if a “vibrational” ponderomotive force is acting on them. Vertically growing Arabidopsis seedlings, subjected to horizontal, saw-tooth shaped oscillations (250 Hz, 1.5 mm amplitude), showed 17±2^o root curvature toward and shoot curvature of 11±3^o against the stronger acceleration. Reversal of the oscillations polarity has lead to curvature direction reversal. Control experiments with starchless mutants (TC7) produced no net curvature, indicating, that dense statoliths were necessary for the observed effect. Thus, the curvature is the plant response to displacement of statoliths by ponderomotive forces, not a touch-induced reaction or another side effect. Protonemata of moss Ceratodon purpureus subjected to the same oscillations have shown displacement of plastids and curvature. Acoustic ponderomotive forces, originating from transfer of a sonic beam momentum due to sound scattering and attenuation in a mechanically heterogeneous system also can displace statoliths. Vertical flax seedlings curved away from the ultrasonic source (800 kHz, 0.1 W/cm²). Besides investigating the graviperception mechanism, vibrational and acoustic forces can serve as tools for analyzing mechanical properties of cell interior and can provide directional stimuli for plants in microgravity.