Hasenstein K H, Kuznetsov O A
Department of Biology, University of Southwestern Louisiana, Lafayette 70504-2451, USA.
Planta. 1999 Mar;208(1):59-65. doi: 10.1007/s004250050534.
Shoots of the lazy-2 mutant of tomato (Lycopersicon esculentum Mill., cv. Ailsa Craig) exhibit negative gravitropism in the dark, but respond positively gravitropically in (red) light. In order to test whether high-gradient magnetic fields (HGMFs) exert only ponderomotive effects on amyloplasts or affect other physiological processes, we induced magnetophoretic curvature in wild-type (WT) and lazy-2 mutant seedlings. Straight hypocotyls of 4-d-old plants were selected and the tips of their hooks were placed in an HGMF near the edge of a magnetized ferromagnetic wedge [grad (H2/2) approximately 10(9)-10(10) Oe2/cm] and mounted on a 1-rpm clinostat. After 4 h in the dark, 85% of WT hypocotyls and 67% of mutant hypocotyls 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 the HGMF was similar for both varieties and resembled the displacement after horizontal reorientation. The WT showed a distinct graviresponse pattern depending on the orientation of the hook, even after excision of the apex. Application of HGMFs to decapitated hypocotyls resulted in curvature consistent with that obtained after horizontal reorientation. After light exposure, decapitated lazy-2 seedlings did not respond positively gravitropically. The data imply that the lazy-2 mutants perceive the displacement of amyloplasts in a similar manner to the WT and that the HGMF does not affect the graviresponse mechanism. The study demonstrates that ponderomotive forces due to HGMFs are useful for the analysis of the gravity-sensing mechanism in plants.
番茄（Lycopersicon esculentum Mill.，品种Ailsa Craig）的lazy - 2突变体的茎在黑暗中表现出负向重力性，但在（红）光下表现出正向重力性反应。为了测试高梯度磁场（HGMFs）是否仅对淀粉体施加磁动力效应或影响其他生理过程，我们在野生型（WT）和lazy - 2突变体幼苗中诱导了磁泳弯曲。选择4日龄植株的直下胚轴，将其弯钩尖端置于磁化铁磁楔边缘附近的高梯度磁场中[grad (H2/2)约为10(9)-10(10)奥斯特平方/厘米]，并安装在1转/分钟的回转器上。在黑暗中放置4小时后，85%的野生型下胚轴和67%的突变体下胚轴向楔弯曲。当幼苗在施加高梯度磁场之前和期间暴露于红光1小时时，78%的野生型幼苗向磁梯度弯曲，但大多数lazy - 2幼苗（75%）背离更强的磁场区域弯曲。两个品种在高梯度磁场中细胞内淀粉体的位移相似，并且类似于水平重新定向后的位移。即使切除顶端后，野生型根据弯钩的方向仍表现出明显的重力反应模式。对去顶下胚轴施加高梯度磁场导致的弯曲与水平重新定向后获得的弯曲一致。光照后，去顶的lazy - 2幼苗没有正向重力反应。数据表明，lazy - 2突变体与野生型以相似的方式感知淀粉体的位移，并且高梯度磁场不影响重力反应机制。该研究表明，高梯度磁场产生的磁动力有助于分析植物的重力感应机制。
