MAGNETOPHORETIC INDUCTION OF CURVATURE IN COLEOPTILES AND HYPOCOTYLS

Coleoptiles of barley (Hordeum vulgare) were positioned in a high grad ient magnetic field (HGMF, dynamic factor del H-2/2 of 10(9)-10(10) Oe (2) cm(-1)), generated by a ferromagnetic wedge in a uniform magnetic field) and rotated on a 1 rpm clinostat. After 4 h 90% of coleoptiles had curved toward the HGMF. The cells affected by HGMF showed clear in tracellular displacement of amyloplasts. Coleoptiles in a magnetic fie ld next to a non-ferromagnetic wedge showed no preferential curvature. The small size of the area of nonuniformity of the HGMF allowed mappi ng of the sensitivity of the coleoptiles by varying the initial positi on of the wedge relative to the coleoptile apex. When the ferromagneti c wedge was placed 1 mm below the coleoptile tip only 58% of the coleo ptiles curved toward the wedge indicating that the cells most sensitiv e to intracellular displacement of amyloplasts and thus gravity sensin g are confined to the top I mm portion of barley coleoptiles. Similar experiments with tomato hypocotyls (Lycopersicum esculentum) also resu lted in curvature toward the HGMF. The data strongly support the amylo plast-based gravity-sensing system in higher plants and the usefulness of HGMF to substitute gravity in shoots.