Dynamics of Cytokinins in Apical Shoot Meristems of a Day-Neutral Tobacco during Floral Transition and Flower Formation¹

Walter Dewitte, Adriana Chiappetta, Abdelkrim Azmi, Erwin Witters, Miroslav Strnad, Jacques Rembur, Michelle Noin, Dominique Chriqui, and Henri Van Onckelen^*

Laboratory for Plant Biochemistry and Physiology, Department of Biology, University of Antwerp, B-2610 Antwerp, Belgium (W.D., E.W., H.V.O.); Laboratory Cytologie Expérimentale et Morphogenèse Végétale, Pierre and Marie Curie University, F-75252 Paris cedex 05, France (A.C., A.A., J.R., M.N., D.C.); and Laboratory of Growth Regulators, Department of Botany, Palacky University and Institute of Experimental Botany, Academy of Sciences of the Czech Republic, 78371 Olomouc, Czech Republic (M.S.)

This study considered cytokinin distribution in tobacco (Nicotiana tabacum L.) shoot apices in distinct phases of development using immunocytochemistry and quantitative tandem mass spectrometry. In contrast to vegetative apices and flower buds, we detected no free cytokinin bases (zeatin, dihydrozeatin, or isopentenyladenine) in prefloral transition apices. We also observed a 3-fold decrease in the content of cytokinin ribosides (zeatin riboside, dihydrozeatin riboside, and isopentenyladenosine) during this transition phase. The group concluded that organ formation (e.g. leaves and flowers) is characterized by enhanced cytokinin content, in contrast to the very low endogenous cytokinin levels found in prefloral transition apices, which showed no organogenesis. The immunocytochemical analyses revealed a differing intracellular localization of the cytokinin bases. Dihydrozeatin and isopentenyladenine were mainly cytoplasmic and perinuclear, whereas zeatin showed a clear-cut nuclear labeling. To our knowledge, this is the first time that this phenomenon has been reported. Cytokinins do not seem to act as positive effectors in the prefloral transition phase in tobacco shoot apices. Furthermore, the differences in distribution at the cellular level may be indicative of a specific physiological role of zeatin in nuclear processes.

Plant Physiol. (1999) 119: 111-122
Copyright Clearance Center:   0032-0889/99/119//12
© 1999 American Society of Plant Physiologists

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