ASGSB 1998 Annual Meeting Abstracts

[63]
GRAVIRESPONSE OF lazy-2 TOMATO SEEDLINGS IS NOT AFFECTED BY CURVATURE-INDUCING MAGNETIC GRADIENTS.   K.H. Hasenstein and O.A. Kuznetsov. Biology Dept., University of SW Louisiana, Lafayette, LA.

Shoots of the lazy-2 mutant of tomato (Lycopersicum esculentum Mill., cv. Ailsa Craig) exhibit a normal negative gravitropic response in the dark, but respond positively gravitropic in (red) light. In order to test whether high gradient magnetic fields (HGMF) exert only ponderomotive effects on amyloplasts or affect other physiological processes, we induced magnetophoretic curvature in wildtype (WT) and lazy-2 mutant seedlings. Straight hypocotyls of four day old plants were selected and the tips of their hooks were placed in a HGMF near the edge of a magnetized ferromagnetic wedge [grad (H²/2)

10⁹-10¹⁰ Oe²/cm] and mounted on a 1-rpm clinostat. After 4 h in the dark 85% of WT hypocotyls and 67% of the mutant curved toward the wedge. When the seedlings were exposed to red light for 1 h prior to and during the application of the HGMF, 78% of the WT seedlings curved toward the magnetic gradient, but the majority of the lazy-2 seedlings (75%) curved away from the stronger field area. Intracellular amyloplast displacement in HGMF was similar for both varieties and resembled the displacement due to horizontal reorientation. The WT showed distinct graviresponse depending on the orientation of the hook, even after excision of the hook. Application of HGMF to decapitated hypocotyls resulted in curvature consistent with that obtained after reorientation. The data imply that the lazy-2 mutants perceive the displacement of amyloplasts similar to the WT and that the HGMF does not affect the graviresponse mechanism. The study demonstrates that ponderomotive forces due to HGMF are useful for the analysis of the gravity sensing mechanism in plants (Supported by NASA grant NAG10-0190).

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