Circadian Rhythmicity in Excised Samanea Pulvini

Abstract

Excised S. saman pulvini were incubated in H2O or 50 mM sucrose in darkness for 100-152 h except for brief exposures to red or far red light, and angles of opening measured periodically. When pulvini are incubated in H2O, the rhythm damps in the open position after 2-3 cycles irrespective of the light treatments, but when sucrose is available, the now persistent oscillations show large red, far red-regulated effects on phase, amplitude, mesor slope and entrainment. Single red light pulses rephase the rhythm, with a phase response curve that resembles that reported for other plants and animals; such rephasing is prevented by immediately subsequent far red light, indicating that phytochrome is the photoreceptor. Red light pulses repeated every 24 h entrain the rhythm, and prevent damping if presented at an appropriate part of the cycle.