Rhythmic Leaflet Movement in Albizzia julibrissin

Abstract

The rhythmic movement of darkened Albizzia leaflets is accompanied by K(+) flux in pulvinule motor cells whose turgor changes control opening and closing. The azide-sensitive open phase is promoted by an increase in temperature from 16 to 33C (Q(10) = 3), implying active transport of K(+) ions during this period. The azide-insensitive closed phase is less temperature-sensitive and has a Q(10) less than 1, implying diffusion or some other physical process as the predominant pathway of K(+) flux at this time. Thus rhythmic leaflet movement is probably due to oscillation in active K(+) transport or membrane permeability or both. External electrolytes (0. 1 n) alter leaflet angle during the open, but not the closed, phase of the rhythm. All chlorides except NH(4) (+) promote opening, with divalent more effective than monovalent ions. Some anions promote and others inhibit opening; activity is not correlated with charge. It is likely that electrolytes alter leaflet movement by altering K(+) flux, accomplishing this by interacting with key macromolecules in motor cell membranes.Pfr phytochrome dampens the amplitude of rhythmic leaflet movement; this process is temperature sensitive (Q(10) = 2) and unaltered by 0.1 n salt solutions. Although K(+) flux is a common basis for phytochrome and rhythmic control of leaflet movement, different mechanisms are clearly involved.