Endogenous Cytokinin Oscillations Control Cell Cycle Progression of Tobacco BY‐2 Cells

Abstract

The significance of cytokinins for the progression of the cell cycle is well known. Cytokinins contribute to the control of the expression of D-cyclins and other cell cycle genes, but knowledge as to how they affect the progression of the cell cycle is still limited. Highly synchronized tobacco BY-2 cells with clearly defined cell cycle stages were employed to determine cytokinin patterns in detail throughout the entire cycle. Concentrations of trans-zeatin, and of some other cytokinins, oscillated during the course of the cell cycle, increasing substantially at all four phase transitions and decreasing again to a minimum value during the course of each subsequent phase. Addition of exogenous cytokinins or inhibition of cytokinin biosynthesis promoted the progression of the cell cycle when the effects of these manipulations intensified the endogenous fluctuations, whereas the progression of the cycle was retarded when the amplitude of the fluctuations was decreased. The results show that the attainment of low concentrations of cytokinins is as important as the transient increases in concentration for a controlled progression from one phase of the cell cycle to the next. Cytokinin oxidase/dehydrogenase activity also showed fluctuations during the course of the cell cycle, the timing of which could at least partly explain oscillations of cytokinin levels. The activities of the enzyme were sufficient to account for the rates of cytokinin disappearance observed subsequent to a phase transition.

Transcriptional Control of the Plant Cell Cycle

“…Cytokinin levels, specifically of trans-zeatin, increase in a very intriguing pattern in the course of cell cycle progression: a broad peak is observed in S-phase and a very transient, and high peak is observed at the G2/M transition (Dobrev et al 2002). Other reports find additional peaks of cytokinin accumulation associated with all cell cycle phase transitions in the tobacco BY2 cell cycle (Hartig and Beck 2005). Furthermore, these striking dynamics of cytokinin accumulation are complemented by fluctuations of cytokinin-degrading cytokinin oxidase activity (Dobrev et al 2002;Hartig and Beck 2005), suggesting that the observed sharp transients are the net result of waves of cytokinin synthesis and degradation.…”

“…Other reports find additional peaks of cytokinin accumulation associated with all cell cycle phase transitions in the tobacco BY2 cell cycle (Hartig and Beck 2005). Furthermore, these striking dynamics of cytokinin accumulation are complemented by fluctuations of cytokinin-degrading cytokinin oxidase activity (Dobrev et al 2002;Hartig and Beck 2005), suggesting that the observed sharp transients are the net result of waves of cytokinin synthesis and degradation. These observations raise the intriguing possibility that fluctuations in cytokinin abundance and perception are an additional oscillating mechanism contributing to overall robustness in plant cell cycle control.…”

Should I fight or should I grow now? The role of cytokinins in plant growth and immunity and in the growth–defence trade-off

“…The levels of cytokinins are known to change during cell cycle progression in cultured plant cells (Redig et al, 1996;Hartig and Beck, 2005). In addition, cytokinin treatment induces the expression of CYCLIN D3 genes in arabidopsis (Riou-Khamlichi et al, 1999), which are conserved regulators of the gap transitions during cell cycle progression in plants and animals.…”

Deep Sequencing of the Medicago truncatula Root Transcriptome Reveals a Massive and Early Interaction between Nodulation Factor and Ethylene Signals

“…CKs regulate the cell cycle in plants (Hartig and Beck, 2005). In legumes CKs function to initiate nodule organogenesis (Gonzalez-Rizzo et al, 2006;Murray et al, 2007;Tirichine et al, 2007;Op den Camp et al, 2011;Plet et al, 2011) and autoregulation of nodulation (Sasaki et al, 2014).…”