Common features of photoperiodism in plants and animals

Abstract— Light break experiments show the role of the circadian clock in photoperiodic timemeasurement. Additional evidence comes from experiments which show the close relation between temperature- or light-induced phase shifts in cycles of photoperiodic responsiveness and simultaneous phase shifts of other processes which are under control of the circadian clock. Using the circadian clock is a common feature of photoperiodism in plants and animals. This clock controls quantitative and qualitative changes in the responsiveness to light. However, quite different pigment systems may be involved, resulting in different action spectra for light break effects. In many cases, these action spectra differ also from the action spectra for phase shifts in the circadian clock.