Phase response curve for the ultradian rhythm of the lateral leaflets of Desmodium gyrans using DC current pulses

In the present study the leaf movement rhythm was perturbed by the applicat ion of DC current pulses (15 muA, 10 seconds, voltage applied: 10 V) to the upper part of the pulvinus, passing through the pulvinus and its stalk. Th e pulses were applied at four different positions of the leaflets: when the leaves were at the lowermost position, when moving up, at the uppermost po sition and when moving down. The pre-perturbed and the post-perturbed rhyth ms were compared. We found that the rhythms were shifted in phase and the p hase shifts observed at the four different positions of the leaflets were s ignificantly different in magnitude as well as direction. Furthermore, we c ould also observe phase advances, which is in contrast to an earlier findin g. A phase response curve (PRC) was constructed to illustrate the sensitivity of the oscillating leaflet system to DC pulses. Substantial delays of about 50 s (as compared to the period of about 200 s) were obtained when pulses were administered at the lowermost position and when leaflet were moving up wards. while advances or no phase shifts were recorded in the uppermost pos ition and when leaflet were moving down respectively.