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 170 h (the onset time tCR-ON) after germination of seeds in natural conditions in a dark incubator. There are no clear cyclic signals in gas exchange before tCR-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 50 h by application of perturbations. This fact may suggest that the circadian rhythms appear via subcritical bifurcation.