In plants, the G2/M control of cell cycle remains an elusive issue as doubts persist about activatory dephosphorylation--in other eukaryotes provided by CDC25 phosphatase and serving as a final all-or-nothing mitosis regulator. We report on the effects of tobacco (Nicotiana tabacum L., cv. Samsun) transformation with fission yeast (Schizosaccharomyces pombe) cdc25 (Spcdc25) on cell characteristics. Transformed cell suspension cultures showed higher dry mass accumulation during the exponential phase and clustered more circular cell phenotypes compared to chains of elongated WT cells. Similar cell parameters, as in the transformants, can be induced in WT by cytokinins. Spcdc25 cells, after cytokinin treatment, showed giant cell clusters and growth inhibition. In addition, Spcdc25 expression led to altered carbohydrate status: increased starch and soluble sugars with higher sucrose:hexoses ratio, inducible in WT by cytokinin treatment. Taken together, the Spcdc25 transformation had a cytokinin-like effect on studied characteristics. However, endogenous cytokinin determination revealed markedly lower cytokinin levels in Spcdc25 transformants. This indicates that the cells sense Spcdc25 expression as an increased cytokinin availability, manifested by changed cell morphology, and in consequence decrease endogenous cytokinin levels. Clearly, the results on cell growth and morphology are consistent with the model of G2/M control including cytokinin-regulated activatory dephosphorylation. Nevertheless, no clear link is obvious between Spcdc25 transformation and carbohydrate status and thus the observed cytokinin-like effect on carbohydrate levels poses a problem. Hence, we propose that Spcdc25-induced higher CDK(s) activity at G2/M generates a signal-modifying carbohydrate metabolism to meet high energy and C demands of forthcoming cell division.
- MeSH
- buněčný cyklus účinky léků genetika fyziologie MeSH
- cytokininy metabolismus farmakologie MeSH
- fungální proteiny genetika fyziologie MeSH
- geneticky modifikované rostliny účinky léků genetika metabolismus MeSH
- kultivované buňky MeSH
- proteiny buněčného cyklu genetika fyziologie MeSH
- ras-GRF1 genetika fyziologie MeSH
- regulace genové exprese u rostlin účinky léků MeSH
- sacharidy analýza MeSH
- Schizosaccharomyces genetika MeSH
- škrob analýza MeSH
- tabák cytologie genetika růst a vývoj MeSH
- transformace genetická MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- cytokininy MeSH
- fungální proteiny MeSH
- proteiny buněčného cyklu MeSH
- ras-GRF1 MeSH
- sacharidy MeSH
- škrob MeSH
Here, the tobacco (Nicotiana tabacum) day-neutral (DN) cv. Samsun transformed with the Schizosaccharomyces pombe mitotic activator gene Spcdc25 was used to study the onset of flowering. Wild type (WT) and cdc25 plants were grown from seeds in vitro until they were 20 cm high. Apical and basal nodes were then subcultured repeatedly and the regenerated plants were used to document time to flowering and the number of leaves formed before flowering. Three sucrose treatments (3, 5 or 7% (weight/volume)) were used and measurements of leaf endogenous soluble carbohydrates were performed. In the 3% treatment, cdc25 plants flowered but WT plants did not. The higher sucrose treatments enabled WT flowering; two-thirds of the plants flowered at 5%, while all plants flowered at 7% sucrose. However, in all treatments, cdc25 plants exhibited significantly earlier flowering and fewer leaves compared with wild type. Remarkably, a typical acropetal flowering gradient in WT plants did not occur in cdc25 plants. In cdc25 leaves, there were significantly higher amounts of endogenous sugars with a higher proportion of sucrose compared with WT. Our data demonstrate that Spcdc25 expression and sucrose act synergistically to induce precocious flowering.
- MeSH
- časové faktory MeSH
- fungální proteiny genetika metabolismus MeSH
- geneticky modifikované rostliny MeSH
- kořeny rostlin růst a vývoj MeSH
- květy účinky léků metabolismus MeSH
- metabolismus sacharidů MeSH
- proteiny buněčného cyklu genetika metabolismus MeSH
- ras-GRF1 genetika metabolismus MeSH
- regulace genové exprese u rostlin MeSH
- sacharosa farmakologie MeSH
- Schizosaccharomyces * genetika MeSH
- tabák účinky léků genetika růst a vývoj metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- fungální proteiny MeSH
- proteiny buněčného cyklu MeSH
- ras-GRF1 MeSH
- sacharosa MeSH
During the last decade, the cell cycle and its control by cyclin-dependent kinases (CDKs) has been extensively studied in eukaryotes. The regulation of CDK activity includes, among others, its activation by Cdc25 phosphatase at G2/M. However, within the plant kingdom studies of this regulation have lagged behind and a plant cdc25 homologue has not been identified yet. Here, we report on the effects of transformation of tobacco (Nicotiana tabacum L., cv. Samsun) with fission yeast (Schizosaccharomyces pombe) cdc25 (Spcdc25) on de novo plant organ formation, a process dependent on rate and orientation of cell division. On shoot-inducing medium (low 1-naphthylacetic acid (NAA), high 6-benzylaminopurine (BAP)) the number of shoots formed on internode segments cultured from transgenic plants was substantially higher than in the non-transformed controls. Anatomical observations indicated that the shoot formation process was accelerated but with no changes in the quality and sequence of shoot development. Surprisingly, and in contrast to the controls, when on root-inducing medium (high NAA, low BAP) cultured segments from transgenic plants failed to initiate hardly any roots. Instead, they continued to form shoots at low frequencies. Moreover, in marked contrast to the controls, stem segments from transgenic plants were able to form shoots even without the addition of exogenous growth regulators to the medium. The results indicate that Spcdc25 expression in culture tobacco stem segments mimicked the developmental effects caused by an exogenous hormone balance shifted towards cytokinins. The observed cytokinin-like effects of Spcdc25 transformation are consistent with the concept of an interaction between cell cycle regulators and phytohormones during plant development.
- MeSH
- cytokininy farmakologie MeSH
- fungální proteiny biosyntéza fyziologie MeSH
- genetická transkripce MeSH
- kořeny rostlin účinky léků růst a vývoj MeSH
- kultivační média MeSH
- kyseliny indoloctové farmakologie MeSH
- proteiny buněčného cyklu biosyntéza fyziologie MeSH
- ras-GRF1 biosyntéza fyziologie MeSH
- RNA biosyntéza MeSH
- Schizosaccharomyces genetika metabolismus MeSH
- tabák účinky léků genetika růst a vývoj MeSH
- výhonky rostlin účinky léků růst a vývoj MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- srovnávací studie MeSH
- Názvy látek
- cytokininy MeSH
- fungální proteiny MeSH
- kultivační média MeSH
- kyseliny indoloctové MeSH
- proteiny buněčného cyklu MeSH
- ras-GRF1 MeSH
- RNA MeSH
