Potassium Flux and Leaf Movement in Samanea saman

Abstract

Phytochrome, a membrane-localized biliprotein whose conformation is shifted reversibly by brief red or far-red light treatments, interacts with the rhythmic oscillator to regulate leaflet movement and potassium flux in pulvinal motor cells of Samanea. Darkened pinnae exposed briefly to red light (high Pf, level) have less potassium in motor cells in the extensor region, more potassium in motor cells in the flexor region, and smaller angles than those exposed to far-red light (low PI, level). Increase in temperature from 24 to 37°increases the differential effect of the light treatments during opening (the energetic phase) but not during closure, implying that phytochrome controls an energetic process. It seems likely that phytochrome interacts with rhythmically controlled potassium pumps in flexor and extensor cells. During nyctinastic closure of white-illuminated pinnae, exposure to far-red light before darkening results in larger angles than does exposure to red. As in rhythmic opening, the angles of all pinnae and the differential effect of the light treatments increases with increasing temperature.

Circadian Rhythmicity in Excised Samanea Pulvini

“…These early events might involve control of ion movements. In Samanea and Albizzia, K+ (13)(14)(15), Cl- (17), and transmembrane potential (10) are regulated by phytochrome and high intensity white light, the latter possibly acting via the same blue absorbing flavoprotein that appears to regulate rhythmic phasing in Neurospora (7,11). A blue absorbing pigment regulates leaflet opening in Albizzia (2,6) and probably in Samanea (3).…”

“…The rhythmic movement of intact Samanea leaflets or of their excised pulvini is affected both by prolonged, high intensity white light (8,13,18) and by brief, low irradiances with R3 or FR absorbed by phytochrome (14,20). Previous investigations on phytochrome photoconversion all involved administration of light during the first 24 hr of darkness following the usual lightdark regimes of plant growth chambers.…”

Circadian Rhythmicity in Excised Samanea Pulvini

“…The rhythmic movement of excised Samanea saman pulvini incubated in H20 or 50 mm sucrose was monitored during extended periods of white light (cool white fluorescent, 2,000 ft-c), darkness, or alternating white Light (16 hr) and darkness (8 hr [18][19][20] possibly related to changes in transmembrane potential (15). Samanea is a particularly useful plant for studies of light-rhythmic interactions, since each pulvinus is an autonomous system whose rhythmic and photoregulated turgor changes persist after the pulvinus has been excised and laminar tissue removed (18,19).…”

“…Samanea is a particularly useful plant for studies of light-rhythmic interactions, since each pulvinus is an autonomous system whose rhythmic and photoregulated turgor changes persist after the pulvinus has been excised and laminar tissue removed (18,19). The photoreceptors and the oscillating system, including the clock and the ions that regulate motor cell turgor and pulvinar movements, must be located in the pulvinus or attached rachilla section.…”

“…The leaflet movement rhythm in Samanea, as in the related plant Albizzia julibrissin, is controlled by differential turgor changes in pulvinal motor cells, in turn regulated by migration of K+ and Cl-ions (16,(18)(19)(20) possibly related to changes in transmembrane potential (15). Samanea is a particularly useful plant for studies of light-rhythmic interactions, since each pulvinus is an autonomous system whose rhythmic and photoregulated turgor changes persist after the pulvinus has been excised and laminar tissue removed (18,19). The photoreceptors and the oscillating system, including the clock and the ions that regulate motor cell turgor and pulvinar movements, must be located in the pulvinus or attached rachilla section.…”