Cultured tobacco mesophyll protoplasts were used as a model to studying the hormonal control of cell-cycle reactivation in plants. Tobacco mesophyll protoplasts were isolated from leaves in which cell division had ceased, and were then cultured. During the first three days in culture, the protoplasts dedifferentiate, resynthesize the cell wall, express wound-related transcripts, and reinitiate the cell cycle. Reinitiation depends on the hormones auxin and cytokinin. I examined the expression of one or two genes related to different aspects of protoplast development. The expression of following genes was examined: wound or stress response (extensin and PR-1a), cell-wall resynthesis (extensin), cytoskeletal reorganization (actin), and cell-cycle reactivation (cdc2, histones H3, and H4). I found that nuclear division began between 30 and 50 hrs of culture about 10-12 hours after the onset of DNA synthesis. By the third day, 70% of the protoplasts had divided. In freshly isolated protoplasts, histones H3 and H4, and cdc2 were not expressed. Expression of cdc2 was activated by 12 hrs of culture, histone expression was activated by 24 hrs concurrent with the initiation of DNA synthesis. Extensin showed a similar pattern of expression as the histones, but expression of PR-1 was activated more slowly. Actin was expressed in leaves and freshly isolated protoplasts, but its expression increased about 4-fold during protoplast culture. When either auxin or cytokinin was omitted from the media, the protoplasts did not divide and the histones and PR-1 were not expressed. Extensin and actin were expressed in the absence of hormones. Hormone delay studies suggested that auxin was required from the beginning of culture, whereas cytokinin was required before the cells enter S-phase. These results are consistent with auxin and cytokinin acting to induce a G$\sb0$ to G$\sb1$ / transition during protoplast development, possibly through initiation of transcription of cell-cycle required genes such as cdc2 and the histones. However, it appears that cdc2 and histone expression are not the primary target of the hormones because their expression is activated 12 hrs or more after the requirement for auxin has passed. Expression of genes associated with cell wall synthesis (extensin) and wounding (extensin and PR-1) do not appear to be required for reactivation of the cell cycle. / Source: Dissertation Abstracts International, Volume: 55-09, Section: B, page: 3665. / Major Professor: George W. Bates. / Thesis (Ph.D.)--The Florida State University, 1994.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_77267 |
| Contributors | Carle, Sigrid Ann., Florida State University |
| Source Sets | Florida State University |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | 126 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
Page generated in 0.0019 seconds