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 (Q10 = 3), implying active transport of K+ ions during this period. The azide-insensitive closed phase is less temperature-sensitive and has a Q10 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 NH4+ 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 (Q10 = 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.
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Selected References
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