We investigated a possible relationship between the levels of reactive oxygen species (ROS) and the stimulation of frond division of the aquatic plant Spirodela polyrrhiza (duckweed) during a 7-day experimental culture period. In particular, we monitored superoxide concentration using a state-of-the-art cell biosensor. A considerable reduction in ROS and superoxide concentration was observed during the first 2 days of culture, whereas duckweed cultures achieved near exponential growth rates after the second day. In addition, apoptotic markers such as the cytoplasmic concentration of cytochrome c, mitochondrial membrane depolarization and the activity of caspase-3 declined during the culture period and at least before daughter frond maturation. We suggest that S. polyrrhiza frond division may have been stimulated by the observed reduction of free radicals and the associated avoidance of cell apoptotic pathways in cultured plants.