Marcus A I, Dixit R, Cyr R J
Department of Biology, Pennsylvania State University, University Park, PA 16802, USA.
Protoplasma. 2005 Dec;226(3-4):169-74. doi: 10.1007/s00709-005-0119-1. Epub 2005 Dec 12.
In most higher-plant cells, cortical microtubules form a tightly focused preprophase band (PPB) that disappears with the onset of prometaphase, but whose location defines the future location of the cell plate at the end of cytokinesis. It is unclear whether the PPB microtubules themselves designate the precise area where the cell plate will insert, or rather if these microtubules are responding to a hierarchical signal(s). Here we show that narrowing of the microtubules within the PPB zone is not necessary for proper division plane determination. In cultured tobacco BY-2 cells in which PPB microtubules are depolymerized, the phragmoplast can still accurately locate and insert at the proper site. The data do not support a role for PPB microtubule narrowing in focusing the signal that is used later by the phragmoplast to position the cell plate; rather, proper phragmoplast positioning is more likely a consequence of a non-microtubule positional element. Although the PPB microtubules do not directly mark the division site, we show that they are required for accurate spindle positioning, an activity that presets the future growth trajectory of the phragmoplast and is necessary for insuring high-fidelity cell plate positioning.
在大多数高等植物细胞中，皮层微管形成一个紧密聚焦的前期带（PPB），该带在有丝分裂前期开始时消失，但其位置决定了胞质分裂末期细胞板的未来位置。目前尚不清楚PPB微管本身是否指定了细胞板将插入的精确区域，或者这些微管是否对分级信号作出反应。在这里，我们表明PPB区域内微管的变窄对于正确确定分裂平面并非必要。在PPB微管解聚的培养烟草BY-2细胞中，成膜体仍然可以准确地定位并插入到合适的位置。这些数据不支持PPB微管变窄在聚焦成膜体后来用于定位细胞板的信号方面的作用；相反，正确的成膜体定位更可能是一个非微管位置元件的结果。虽然PPB微管不直接标记分裂位点，但我们表明它们对于精确的纺锤体定位是必需的，纺锤体定位活动预设了成膜体未来的生长轨迹，并且对于确保高保真细胞板定位是必要的。
