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DIRECT EVIDENCE OF ASSOCIATION BETWEEN PROTON EFFLUX AND BENDING OF ARABIDOPSIS ROOT UNDER GRAVISTIMULATION.  Y. Xu, E. Johannes and N.S. Allen. Department of Botany, North Carolina State University, NC.

   Rapid changes in cytosolic pH within specific columella cells in the Arabidopsis root tip have been demonstrated and these changes clearly play a role in early perception of changes in the gravity vector.  Proton fluxes surrounding the distant elongation zone of gravistimulted Arabidopsis seedlings have been investigated using the Non-Invasive Ion Selective Probe.  3~4-day old sterilized seedlings were mounted in a 3D Measurement Chamber (3DMC), which allowed the seedlings to be moved in a 3D fashion and to be viewed in both top view (x/y axis) and side view (y/z axis) so that the relative position between the probe and the seedling can be precisely defined. The seedlings were mounted on the 3DMC in such a way that the main axis of their root was perpendicular to the ground level. Gravistimulation was achieved by turning the seedlings 90 degree. The roots started to bend after ca. 30 mins. Two proton probes were used simultaneously to measure the proton fluxes of both upper and lower sides of the bending region. The results indicate that proton effluxes occur on both sides of the root with a flux two times larger on the upper side. This implies that a more acidic environment is associated with the more active elongation areas the upper part of the root.

(Supported by NASA grant NAGW 4984.)

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