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Abstract:
The leaves of Desmodium gyrans (L.F.) DC show circadian movements in the terminal and ultradian movements of the lateral leaflets. The
movements are due to swelling and shrinking of motor cells in special organs. The anatomy of these pulvini is described for the lateral leaflets. Data
from electrophysiological recordings using microelectrodes inserted into the lateral pulvini, together with treatments that affect the proton pumps and
ion channels, have been used to develop a physiological model of the ultradian leaflet movement. It explains the oscillations in the motor cells as being
due to a change between a pump state and depolarization. During the pump state, ions are taken up, causing water influx and swelling of the motor
cells. Depolarization causes loss of ions and water efflux (the motor cells shrink). The roles of calcium and the phosphatidyl inositol signal chain are
discussed on the basis of experiments using chemical agents that affect these processes. Since calcium oscillations are known to occur in organisms
in both time and space, an attempt has been made to simulate the situation in Desmodium pulvini by a model of specially coupled oscillators. Effects of
different other treatments of the lateral pulvini are discussed. Oscillations in the minute range seem to be more common and some might be related to
turgor regulation and ion uptake comparable to the situation in Desmodium. The ultradian control of the lateral pulvini and the circadian control of the
terminal pulvini are apparently based on different mechanisms.
