A feedback model for biological rhythms. II. Comparisons with experimental results, especially on the petal rhythm of Kalanchoë

Abstract

Parameters of a previously published feedback model are determined for the 24 hour petal rhythm of Kalanchoë blossfeldiana. This is done by using results from phase shift experiments on this plant, the phase shifts being caused by light perturbations. With these parameters the model and the plant rhythm itself show not only similar phase shifts but also similar changes in amplitude after a light perturbation. Effects of two consecutive light perturbations can then be predicted from the model. The importance of such experiments is emphasized as they provide a basis for discussions on entrainment phenomena. "Reversing" and "decreasing transients" as well as a so-called "singular state" (a non-oscillatory state) are known from experimental studies of biological 24-hour rhythms. It is shown that these phenomena are general features of the feedback model and can be observed not only in the Kalanchoë version. The feedback model is also discussed in relation to rhythms with shorter periods e.g. rhythmic growth movements in young sunflower plants. In oat plants with rhythmic water output from the leaves it is shown that a light perturbation causes roughly the same phase shift as a dark perturbation given half a period later. This is also predicted by the model. Finally, calculations are presented showing that results of phase shift experiments on a single oscillator cannot always be directly applied to a population of non-interacting oscillators with slightly different free-running periods. © 1972.