Ruth L. Satter

Potassium Flux: a Common Feature of Albizzia Leaflet Movement Controlled by Phytochrome or Endogenous Rhythm

Leaflets close when potassium moves into dorsal and out of ventral pulvinule motor cells and open when the flux direction is reversed. This is true whether leaflet movement is controlled by an endogenous rhythm or by phytochrome.

LIGHT, CLOCKS AND ION FLUX: AN ANALYSIS OF LEAF MOVEMENT

This chapter discusses phytochrome-controlled leaf movements, which maximize several advantages within a single biological system. Leaf movements in Albizzia and Samanea are reasonably rapid and easy to monitor and are an accurate indicator of K + flux and, thus, of membrane properties. They also have measurable electrical components, are amenable to some types of biochemical analysis, and show interaction with rhythmic phenomena. The chapter presents a summary of the conclusions of the earlier investigations on this subject. The combined physiological, chemical, and electrical data on leaf movements in Albizzia and Samanea reinforce the view that some membrane-localized process, such as ion transport, is an early consequence of phytochrome phototransformation. The fact that rhythmic and blue light-mediated processes also regulate ion movements and changes in electrical potential suggests the possibility that all of these phenomena and their interactions are the result of membrane-based changes.

Pfr PHYTOCHROME AND SUCROSE REQUIREMENT FOR RHYTHMIC LEAFLET MOVEMENT IN ALBIZZIA

Abstract— Albizzia leaflets open and close with a circadian periodicity without damping during extended dark periods if supplied with sucrose and irradiated with red each rhythmic cycle. In the absence of a carbohydrate source, the rhythm damps irrespective of phytochrome status and the differential effects of red and far‐red light treatments tend to disappear after 2 or 3 cycles. The rhythm also damps if leaflets are exposed to red only once, or if they are exposed to far‐red once or cyclically. Sucrose does not prevent such damping but affects the stable angle assumed; the rhythm damps in the closed position in the presence of sucrose, and in the partially open position in its absence. Sucrose appears to have two distinct effects; it interacts with Pfr to promote manifestation of the rhythm and it reduces the average angle, whether the Pfr level is low or high.

Vanadate inhibition of phytochrome effects on leaflet movement in Albizzia julibrissin

Abstract A previous report revealed that the transport inhibitor sodium vanadate interferes with the rhythmic closure of Albizzia julibrissin leaflets during an extended dark period. Vanadate (0.5–1.0 mM) also prevents phytochrome conversion from affecting the movements, acting selectively on leaflets whose phytochrome is in the P fr form. Leaflet closure following transfer from white light to darkness is inhibited to a similar extent by vanadate or by brief far-red pre-irradiation, while leaflet opening during an extended dark period is promoted by vanadate or by brief far-red irradiation, although the kinetics of movement under the latter two conditions differ from each other. Sodium monophosphate, by contrast, promotes the closure of leaflets transferred directly from white light to darkness, but it does not affect the closure of far-red pre-irradiated leaflets, or the rhythmic opening of either far-red irradiated or non-irradiated leaflets. It is not known whether vanadate inhibits a primary action of P fr or a later reaction in the chain of events that link leaflet movement to phytochrome conversion.