title: Local expression of the ipt gene in transgenic tobacco (Nicotiana tabacum L. cv. SR1) axillary buds establishes a role for cytokinins in tuberization and sink formation.
abstract: The developmental characteristics of a transgenic tobacco line (BIK62) expressing the ipt cytokinin-biosynthetic gene under the control of a tagged promoter were analysed. In situ hybridization and cytokinin immunocytochemistry revealed that the ipt gene was mainly expressed in the axillary buds after the floral transition. The ipt-expressing axillary buds presented morphological alterations such as short and narrow scale-leaflets, and swollen internodes filled with starch grains, giving rise to short and tuberized lateral branches. In addition, the modification of the endogenous cytokinin balance in the axillary meristems resulted in a fast rate of leaf initiation and cytokinins accumulated mostly in the lateral zones of the reactivated axillary meristems, suggesting a role in leaf organogenesis. Cell cycle analysis revealed that the reactivated axillary meristems were characterized by predominant S+G2 nuclei. Terminal internodes displayed low levels of hexose and sucrose concomitant with starch accumulation. Extracellular invertases (EC 3.1.26) were also present in higher amounts in the tuberizing internodes compared to the axillary buds of wild-type tobacco. These results underline the role of cytokinins in cell cycle regulation and in the creation of a sink--source effect. They also provide new information about cytokinin involvement in the process of tuberization and their overproduction in axillary buds giving rise to tuberized lateral branches in a naturally non-tuberizing species.
authors.affiliation: University Pierre and Marie Curie, Laboratory CEMV, Bât. N2, 4, place Jussieu, F-75252 Paris Cedex 05, France. anne.guivarch@snv.jussieu.fr
authors.forename: Anne
authors.initials: A
authors.lastname: Guivarc'h
authors.forename: Jacques
authors.initials: J
authors.lastname: Rembur
authors.forename: Marc
authors.initials: M
authors.lastname: Goetz
authors.forename: Thomas
authors.initials: T
authors.lastname: Roitsch
authors.forename: Michèle
authors.initials: M
authors.lastname: Noin
authors.forename: Thomas
authors.initials: T
authors.lastname: Schmülling
authors.forename: Dominique
authors.initials: D
authors.lastname: Chriqui
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics* / Q000378:metabolism; D050260:Carbohydrate Metabolism; D002455:Cell Division / Q000235:genetics / Q000502:physiology; D003583:Cytokinins / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D006026:Glycoside Hydrolases / Q000378:metabolism; D006601:Hexoses / Q000378:metabolism; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D018519:Meristem / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D010641:Phenotype; D010710:Phosphates / Q000378:metabolism; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D018547:Plant Stems / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D030821:Plants, Genetically Modified; D013213:Starch / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism; D014026:Nicotiana / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D043324:beta-Fructofuranosidase
chemical_list: D003583:Cytokinins; D006601:Hexoses; D010710:Phosphates; D013395:Sucrose; D013213:Starch; D019883:Alkyl and Aryl Transferases; C023197:tRNA isopentenyltransferase; D006026:Glycoside Hydrolases; D043324:beta-Fructofuranosidase