The role of the cell wall in nuclear positioning in plant cells

1.在NAA和苄基腺嘌呤存在下培养的球形间期烟草BY-2细胞中，细胞核出现在细胞的中央区，细胞质中有肌动蛋白细丝，但没有微管。Cyclasin破坏胞质链中的肌动蛋白细丝会改变核的位置，但丙酰胺破坏微管不会改变核的位置。从这些发现，我们得出结论，肌动蛋白细丝，而不是微管，参与了决定间期烟草BY-2细胞中细胞核的位置。在从烟草BY-2细胞分离的原生质体中，细胞核位于原生质体的中央区域。但是，随着原生质体再生细胞壁，细胞核的位置从中央区域改变到细胞外围。这种核迁移被纤维素生物合成抑制剂2，6-二氯苯腈抑制。由于用2，6-二氯苯甲腈处理的原生质体不能再生细胞壁，因此我们得出结论，细胞壁的存在是细胞核从中央区域迁移到细胞外围所必需的。在2，4-D存在下培养的有丝分裂前烟草BY-2细胞中，细胞核存在于细胞的中央区域，由包含作用丝和微管的细胞质链连接。无论是细胞抑制素对肌动蛋白细丝的破坏，还是丙酰胺对微管的破坏，都不会改变细胞核的位置。只有当肌动蛋白细丝和微管都断裂时，细胞核才会改变其位置。根据这些结果，我们得出结论，肌动蛋白细丝和微管都参与了有丝分裂前烟草BY-2细胞的核定位。

1. In spherical interphase tobacco By-2 cells cultured in the presence of NAA and benzyl-adenine, the nucleus is present in the central region of the cell being tethered by the cytoplasmic strands in which actin filaments are present, but microtubules are not. The disruption of actin filaments in the cytoplasmic strands by cytochlasin alters the position of the nucleus, but that of microtubules by propyzamide does not alter the position of the nucleus. From these findings, we reach the conclusion that actin filaments, but not microtubules, are involved in determining the position of the nucleus in interphase tobacco BY-2 cells.2. In protoplasts isolated from tobacco BY-2 cells, the nucleus is present in the central region of the protoplast. But, as the protoplasts regenerate cell walls, the nucleus changes its position fom the central region to the cell periphery. This nuclear migration is inhibited by 2,6-dichlorobenzonitrile, an inhibitor of cellulose biosynthesis. As pro-toplasts treated with 2,6-dichlorobenzonitrile do not regenerate cell walls, we reach the conclusion that the presence of the cell wall is necessary for the nucleus to migrate from the central region to the cell periphery.3. In premitotic tobacco BY-2 cells cultured in the presence of 2,4-D, the nucleus is present in the central region of the cell being tethered by the cytoplasmic strands which contain both action filaments and microtubules. Neither the disruption of actin filaments by cytochlasin nor that of microtubules by propyzamide alters the position of the nucleus. The nucleus changes its position only when both actin filaments and microtubules are dis-rupted. From these results we reach the conclusion that both actin filaments and micro-tubules are involved in the nuclear positioning in premitotic tobacco BY-2 cells.