All in good time: the Arabidopsis circadian clock

Biological time-keeping mechanisms have fascinated researchers since the mo vement of leaves with a daily rhythm was first described >270 years ago. Th e circadian clock confers a similar to 24-hour rhythm on a range of process es including leaf movements and the expression of some genes. Molecular mec hanisms and components underlying clock function have been described in rec ent years for several animal and prokaryotic organisms, and those of plants are beginning to be characterized. The emerging model of the Arabidopsis c lock has mechanistic parallels with the clocks of other model organisms, wh ich consist of positive and negative feedback loops, but the molecular comp onents appear to be unique to plants.