Rhythmic Leaf Movements under Physical Loading of the Leaves

Abstract

Abstract The effect of physical loading on period and amplitude of the ultradian oscillating leaflets of Codariocalyx motorius (= Desmodium gyrans) and the circadian oscillating leaves of Oxalis regnellii was investigated. In Codariocalyx the leaflets were loaded with pieces of copper thread which were clamped to the leaflet. Weights of the loads varied from 3 to 12 mg, and a typical leaflet is 1.5 mg. In about 80% of the cases we recorded an increase of the period length due to the loading in the order of 10% (the period length is typically 3-4 min). The amplitude was lowered in all the cases, the magnitude depending on the size of the weight used. In most of the cases, when not too heavily loaded, both amplitude and period returned to (or close to) the previous value when the leaflets were unloaded. In Oxalis the leaves were loaded with metal clips fixed to the leaflets at the midrib position. All three leaflets on a stalk were loaded. The clips used weighed 390 ± 0.4. 640 ± 6 and 810 ± 4 mg respectively, and a typical leaflet is 91 ± 4 mg. For the heaviest weights at least, this resulted in a lowering of the amplitude, but the oscillations continued, and we could not observe any effect on the period of the rhythmic movements.