Competency of Nicotiana tabacum L. stem tissues to dedifferentiate is associated with differential levels of cell cycle gene expression and endogenous cytokinins.
The expression of the mitotic cyclin Arath; CYCB1;1 and of the cyclin-dependent kinase Arath; CDC2a was located by beta-glucuronidase histochemical detection and in situ hybridization, and was quantified by 4-methylumbelliferyl beta- D-glucuronide assay in tobacco stem tissues during both in vivo differentiation and in vitro dedifferentiation. The changes in localization of endogenous cytokinins were also determined during both processes using quantitative analysis and in situ immunocytochemistry. The CDC2a promoter was expressed continuously during stem development, with particularly high expression in the shoot apical meristem and in the internal and external primary phloem. CYCB1 expression was not restricted to the dividing cells; its expression in the shoot apical meristem was particularly high in the leaf-forming peripheral cells but the gene was also expressed throughout development in the internal and external phloem in which the rate of cell division was reduced or zero. Following in vitro culture, the internal phloem cells appeared to be particularly competent to re-enter the cell cycle within a short lag phase while the pith tissue reactivated later. In culture, cells that resumed division were found to accumulate cytokinins. The high competency of primary phloem to dedifferentiate was associated with its capacity to express CDC2a and CYCB genes and the presence of high cytokinin levels, providing some insights into the determinants of competency for resuming cell division.
Boucheron
E
E
Université Pierre et Marie Curie, Laboratoire CEMV, Bât N2, 4 place Jussieu, 75252 Paris Cedex O5, France.
Guivarc'h
A
A
Azmi
A
A
Dewitte
W
W
Van Onckelen
H
H
Chriqui
D
D
D017360:Arabidopsis / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics; D016203:CDC2 Protein Kinase; D002453:Cell Cycle / Q000235:genetics*; D002454:Cell Differentiation / Q000235:genetics*; D019926:Cyclin B / Q000235:genetics; D018844:Cyclin-Dependent Kinases / Q000235:genetics; D003583:Cytokinins / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D005966:Glucuronidase / Q000235:genetics / Q000378:metabolism; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007210:Indoleacetic Acids / Q000378:metabolism; D018519:Meristem / Q000235:genetics; D010940:Plant Proteins / Q000378:metabolism; D018547:Plant Stems / Q000166:cytology / Q000235:genetics*; D030821:Plants, Genetically Modified; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics* / Q000378:metabolism
D029681:Arabidopsis Proteins; C462528:CycB1 protein, Arabidopsis; D019926:Cyclin B; D003583:Cytokinins; D007210:Indoleacetic Acids; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; C030737:indoleacetic acid; D016203:CDC2 Protein Kinase; C418966:CDC2A protein, Arabidopsis; D018844:Cyclin-Dependent Kinases; D005966:Glucuronidase