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Abstract: Higher plants respond to environmental stresses by a sequence of reactions which include the reduction of growth by affecting cell division. It has been shown that calcium ions plays a role as a second messenger in mediating various defence responses under environmental stresses. In this study, the role of calcium ions on cell cycle progression under abiotic stresses has been examined in tobacco BY-2 suspension culture cells. Using synchronized BY-2 cells expressing the endogenous calcium sensor aequorin as experimental system, we could show that oxidative and hypoosmotic stress both induce an increase of intracellular calcium and cause a delay of the cell cycle. The inhibitory effect of these abiotic stress stimuli on cell cycle progression could be mimicked by increasing the intracellular calcium concentration via application of an external electrical field. Likewise, depletion of calcium ions in the culture medium suppressed the effect of the stimuli tested. These results demonstrate that calcium signalling is involved in the regulation of cell cycle progression in response to abiotic stress. [Copyright &y& Elsevier]