ASGSB 1999 Annual Meeting Abstracts

MAGNETOPHORETIC ANALYSIS OF THE GRAVISENSING SYSTEM OF CHARA. O.A. Kuznetsov and K.H. Hasenstein. Biology Dept., Univ. of SW Louisiana, Lafayette. LA.

The viscoelastic properties of the cytoplasm and the plastid-based gravisensing of Chara rhizoids were analyzed by observing the displacement of statoliths inside grown rhizoids. The statoliths were lifted by high gradient magnetic fields (HGMF) that acted against gravity. We studied the viscoelastic properties by the extent and rate of statoliths displacement under different force values and determined the effect of statoliths displacement on directional growth. Lateral displacement of statoliths by magnetic forces lead to curvature of the rhizoid in the direction of the displacement. The contribution of the cytoskeleton to the viscoelasticity of the cytoplasm and positioning of the statoliths was assayed by videomicroscopy before and after depolymerizing microtubules (5 µM oryzalin) or f-actin (< 1 µM lactrunculin B). Application of oryzalin did not change the organization of the cell apex or gravimagnetophoretic behavior of statoliths or rhizoid growth. However after ca. 3 hours the typically longitudinal cytoplasmic streaming in the basal portion of the cell separated into independent complexes that rotated perpendicular to the cell axis and the growth rate gradually declined to zero. Lactrunculin treatment immediately stopped growth of rhizoids and within minutes the statoliths sedimented to the apex. After magnetophoretic upward movement, the rate of sedimentation due to gravity in lactrunculin-exposed rhizoids decreased insignificantly but the saltatory movements of the plastids were dramatically reduced. Despite the effect on statoliths, the cytoplasmic streaming in the basal portion of the cell was not completely disrupted, indicating that lactrunculin affects rhizoid displacement more than cytoplasmic streaming. Combining oryzalin and lactrunculin B enabled even greater upward displacement of statoliths by magnetic forces but not beyond the nucleus, indicating that the periphery of the nucleus was unaffected by cytoskeletal inhibitors

(Supported by NASA:NAG10-0190).

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