title: Cell cycle regulation by plant growth regulators: involvement of auxin and cytokinin in the re-entry of Petunia protoplasts into the cell cycle.
abstract: In order to understand the mode of action of auxins and cytokinins in the induction of cell division, the effects of the two plant growth regulators 2,4-dichlorophenoxyacetic acid (2,4-D) and N6-benzyladenine (BA) were investigated using mesophyll protoplasts of Petunia hybrida, cultivated in either complete medium or in medium deficient in cytokinin, auxin or both. Firstly we studied DNA synthesis, using 5-bromodeoxyuridine/bisbenzimide Hoechst/propidium iodide flow cytometry analyses and by the monitoring of histone H4 transcript levels. Roscovitine, a cyclin-dependent kinase (CDK) inhibitor, was found to block the cell cycle prior to entry into the S and M phases in the cultured P. hybrida protoplasts. This suggests that in Petunia cell there is a requirement for CDK activity in order to complete the G1 and G2 phases. Further experiments using roscovitine showed that neither 2,4-D nor BA were individually able to induce cell cycle progression beyond the roscovitine G1 arrest. We also monitored the phytohormonal induction of S phase by studying variations in transcript levels of the gene for mitogenactivated protein kinase (PMEK1) and transcript levels of the cell division cycle gene cdc2Pet. Only 2,4-D, and not BA, was able to stimulate PMEK1 gene transcription; thus, the more rapid S-phase induction in 2,4-D-treated protoplasts may be attributable to the activation of this transduction pathway. In contrast, both plant growth regulators were required to induce the appearance of cdc2Pet mRNA transcripts prior to S-phase engagement.
authors.affiliation: Institut de Biotechnologie des Plantes, CNRS ERS 569, Université de Paris-Sud, Orsay, France. trehin@ibp.u-psud.fr
authors.forename: C
authors.initials: C
authors.lastname: Tréhin
authors.forename: S
authors.initials: S
authors.lastname: Planchais
authors.forename: N
authors.initials: N
authors.lastname: Glab
authors.forename: C
authors.initials: C
authors.lastname: Perennes
authors.forename: J
authors.initials: J
authors.lastname: Tregear
authors.forename: C
authors.initials: C
authors.lastname: Bergounioux
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000494:pharmacology; D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D001593:Benzyl Compounds; D016203:CDC2 Protein Kinase / Q000037:antagonists & inhibitors / Q000235:genetics; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics; D002453:Cell Cycle / Q000187:drug effects*; D003583:Cytokinins / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000494:pharmacology*; D007701:Kinetin; D008969:Molecular Sequence Data; D059828:Plant Cells; D010937:Plant Growth Regulators / Q000494:pharmacology*; D010944:Plants / Q000187:drug effects* / Q000235:genetics; D011523:Protoplasts / Q000187:drug effects / Q000378:metabolism; D011687:Purines / Q000494:pharmacology; D000077546:Roscovitine
chemical_list: D001593:Benzyl Compounds; D003583:Cytokinins; D004791:Enzyme Inhibitors; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D011687:Purines; D000077546:Roscovitine; D015084:2,4-Dichlorophenoxyacetic Acid; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D016203:CDC2 Protein Kinase; D000225:Adenine; C480551:benzylaminopurine; D007701:Kinetin