ASGSB 1999 Annual Meeting Abstracts

MAGNETOPHORETIC INDUCTION OF CURVATURE IN THE INFLORESCENCE STEMS OF ARABIDOPSIS. S.E. Weise¹, O.A. Kusnetsov², K.H. Hasenstein², and J.Z. Kiss¹. ¹Miami University, Oxford OH 45056 and ²Univ. SW Louisiana, Lafayette, LA

Gravitropic sensing in inflorescences of both wild-type and starch-deficient mutants of Arabidopsis appears to depend upon the endodermis. Since the endodermis runs the entire length of the inflorescence stem, the precise site of gravisensing along the stem is difficult to define. To investigate gravisensitivity and transduction along the stems, we positioned 25-30 mm long inflorescence stems of Arabidopsis in a high gradient magnetic field (HGMF, dynamic factor H2/2 of 10⁹-10¹⁰ Oe² cm^-1) generated by a ferromagnetic wedge in a uniform magnetic field and rotated at 1 rpm on a clinostat for a minimum of 5 hours. When the wedge was placed 0-5 mm from the apex of the inflorescence stem, 49% of the WT stems curved toward the HGMF. Furthermore, when the HGMF was applied to the apical elongation zone (6-10 mm from the apex), 31% of the stems curved toward the HGMF. Positioning the wedge in the mid-elongation zone (11-15 mm from the apex) resulted in 46% of the inflorescence stems curving toward the HGMF.  Exposure of the basal elongation zone (16-20 mm from the apex) to the HGMF resulted in 38% of the stems curving toward the HGMF. When the inflorescence stems responded to the HGMF, the site of curvature was limited to the vicinity of the wedge.  In contrast, when the wedge was placed in the basal region (> 35 mm from the apex) of longer inflorescence stems, no curvature was observed. The lack of curvature may be due to higher rigidity of the basal region of longer stems as a result of the deposition of lignin and other cell wall components.  As a control, similar experiments were preformed with a starchless (phosphoglucomutase) mutant. When the HGMF was applied to the mid-elongation zone, only 5% of the stems curved toward the HGMF.  Based on these results, we conclude that sensing is diffuse along the entire length of the inflorescence stem with a limited spatial distribution of the signal resulting from a starch-dependent graviperception.

(Supported by NASA grants NAG 2-1017 to JZK and NAG10-0190 to KHH).

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