EFFECTS OF LANTHANUM ON RHYTHMIC AND NYCTINASTIC LEAFLET MOVEMENTS INALBIZZIA-LOPHANTHA

The involvement of extracellular calcium in rhythmic and nyctinastic m ovement of Albizzia Iophantha Benth. leaflets has been studied by test ing the effect of LaCL(3) and its interaction with the phytochrome con trol of these movements. A 2 h pulse of LaCL(3) (10-50 mM) promotes a loss of rhythmicity, leaving leaflets in an open position, and also ov errides the phase shift caused by phytochrome. A 2 h pulse of LaCl3 (1 mM) decreases the amplitude of rhythmic oscillations but does not pro mote arhythmicity nor modify the phase shift caused by red light. The red light pulse abolishes the damping effect of 1 mM La3+. LaCl3 inhib its nyctinastic closure and decreases the phytochrome control of nycti nastic closure. A subsequent supply of CaCl2 (10 to 100 mM) does not r everse La3+ (10 mM) inhibition of closure. Light-induced opening is in dependent of LaCl3 but rhythmic opening in darkness shows different re sponses to La3+ depending on the time at which La3+ is applied. Data s uggest that extracellular calcium is required for the closure mechanis m and for the expression of rhythmic movement. It could also be involv ed in the phytochrome transduction pathway and/or in the linking steps between phytochrome and the circadian clock.