Circadian rhythm formation in plant seedling: global synchronization and bifurcation as a coupled nonlinear oscillator system.

Circadian rhythm formation is studied in seedlings after germination measuring their respiratory metabolism. The circadian rhythm is clearly observed at about 170h (the onset time t(CR-ON)) after germination of seeds in natural conditions in a dark incubator. There are no clear cyclic signals in gas exchange before t(CR-ON). Application of external triggers (temperature shocks) near the onset of the rhythm in seedling growth strongly affects formation processes. The onset is shifted earlier up to 50h by application of perturbations. This fact may suggest that the circadian rhythms appear via subcritical bifurcation.