Basic properties of the circadian leaf movements of Oxalis regnellii, and period change due to lithium ions

The circadian leaf movement of Oxalis regnellii Mig, has been investigated. The three leaflets of a stalk were normally synchronized, and under the experimental conditions chosen they showed a period of 26.2 ± 0.1 h. Cutting off one or two leaflets led to a successive decrease of the period length (25.7 ± 0.1 and 25.1 ± 0.3 h resp.). It was possible to phase shift the leaf movements by mechanical means (advance of 1.6 ± 0.3 h). Lithium ions, added permanently to the transpiration stream, increased the period length of the leaf movements by more than one hour (with 10 m M Li + ). A 24 h pulse of 20 m M LiCl caused a permanent 2–3 h phase delay of the circadian rhythm. Four‐h pulses, on the other hand, provoked only transient phase delays, the magnitude being dependent on the phase of application. Lithium concentrations were determined for different regions of leaves and pulvini. It was shown that leaf segments had considerably lower concentrations than pulvini. No significant difference in the lithium concentration was observed between the upper and lower part of pulvini. In the light leaf position was strongly correlated with water uptake and the consequences for applications of substances to the circadian system via the transpiration stream is discussed. A simple model of the oscillatory system and reactions connected to it is discussed.