Hormonal Control of the Plant Cell Cycle
Though highly developmentally programmed, cell division in plant cells is readily susceptible to external factors. Promotion and integration of signals from both developmental programs and environmental stimuli are often mediated by plant hormones. Althou
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1 Introduction Though highly developmentally programmed, cell division in plant cells is readily susceptible to external factors. Promotion and integration of signals from both developmental programs and environmental stimuli are often mediated by plant hormones. Although cytokinins and auxins have long attracted most attention because of their tremendous effects on cell division, a certain body of evidence is building on the involvement of other plant hormones in different aspects of the plant cell cycle. A wealth of data on the role of phytohormones during the plant cell cycle has been generated through the use of the Nicotiana tabacum cv. Bright Yellow 2 (BY-2) derived cell culture as a model system (Nagata et al. 1992). The extent to which BY-2 cells can be synchronised (Nagata and Kumagai 1999) has been proven essential for the detection of short-lived surges in cytokinin levels during the cell cycle (Redig et al. 1996). Tobacco BY-2 cell cultures are also regularly used as a model system to study the mode of action of abscisic acid (ABA) and jasmonates (JA, MeJA), two plant hormones often linked to stress responses. It is frequently observed that stress signals not only induce typical stress responses, but also negatively affect growth rate and cell division.
2 Cytokinins Because of their cytokinin autotrophic nature, BY-2 cells have played a pivotal role in the study of cytokinin kinetics during the plant cell cycle. Similar to data from N. tabacum cv. Xanthi XD6S cells (Nishinari and Syono 1986), analysis of cytokinin accumulation during cell cycle progression in N. tabacum cv. BY-2 (Redig et al. 1996; Laureys et al. 1999) revealed transient peaks in the concentration of zeatin-type cytokinin species at early G1, G1 to early S, late S and G2/M transition. Less abundant peaks of dihydrozeatin-type cytokinins 1
Laboratory of Plant Biochemistry and Physiology, Department Biology, University of Antwerp (UIA), Universiteitsplein 1, 2610, Antwerp, Belgium
Biotechnology in Agriculture and Forestry, Vol. 53 Tobacco BY-2 Cells (ed. by T. Nagata, S. Hasezawa, and D. Inzé) © Springer-Verlag Berlin Heidelberg 2004
Hormonal Control of the Plant Cell Cycle
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were observed at G1 and early S, and at G2/M transition. In both cases, the free base form peaks were accompanied by ribotide form and riboside form peaks. Neither O-glucosides nor N-glucosides appeared to change dramatically during the cell cycle. The concentration of isopentenyladenine-type (iP) cytokinins either showed no changes during cell cycle progression, or was below detection limit. A similar study (Dobrev et al. 2002) did find clear iP-type cytokinin (at early S-phase) and zeatin-type O-glucoside (at G2/M) peaks. In addition, the zeatin-type cytokinin peak in S-phase appeared in mid rather than in late S-phase. The sharp and abundant premitotic peak in zeatin-type cytokinins was, however, seen in all studies. Dobrev and coworkers (2002) detected both cis- and trans-zeatin in this premitotic cytokinin peak and suspect a fine regulation of endogenous
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