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

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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.