ASGSB 1998 Annual Meeting Abstracts

[59]
AMYLOPLAST MAGNETOPHORESIS MIMICS GRAVITROPISM IN SINGLE-CELL GRAVISENSING MOSS PROTONEMATA. O.A. Kuznetsov¹, J. Schwuchow², F.D. Sack², K.H. Hasenstein¹. ¹Biology Dept., University of SW Louisiana, Lafayette, LA 70504-2451 & ²Dept. of Plant Biology, Ohio State University, Columbus, OH 43210.

After gravistimulation of Ceratodon purpureus protonemata in the dark, amyloplast sedimentation is followed by upward curvature in the wild-type (WT) and downward curvature in the wrong way response (wwr) mutant. Both gravity sensing and the response take place in the same apical cell. We used high gradient magnetic fields (HGMF) to displace the amyloplasts inside protonemata and to simulate the effect of gravity. The field was applied by placing protonemata either between two permanent magnets at the edge of the gap, or close to the edge of a magnetized ferromagnetic wedge, or close to a small (< 1 mm) permanent magnet. Continuous application of an HGMF in all three configurations resulted in plastid displacement and induced curvature in tip cells of WT and wwr protonemata. Generally, WT cells curved toward the HGMF, and wwr cells away from the HGMF, comparable to gravitropism. Plastids isolated from protonemal cultures had densities ranging from 1.24 to 1.38 g/cm³. Plastid density was similar for both genotypes, but the mutant contained larger plastids (diameter [±SE] = 1.97±0.03 µm) than the WT (1.74±0.03 µm), possibly explaining the stronger response of the wwr protonemata to HGMFs. These data support the plastid-based theory of gravitropic sensing and suggest that HGMF-induced ponderomotive forces can provide a gravity-like stimulus (supported by NASA grants NAG10-0179 [FS] & NAG10-0190 [KHH])

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