LIGHT-PULSES AND INJECTION OF IP3 INDUCE MATING ABILITY IN PARAMECIUM-BURSARIA

Populations of cells of Paramecium bursaria exposed to a light-dark cy cle (LD; 12:12 hr) show mating reactivity during the light period but not during the dark period, After transfer to constant light (LL) or c onstant darkness (DD), they continue to show a circadian rhythm of mat ing reactivity. When cells in the non-reactive phase of DD were expose d to light pulse (from 5 sec to 6 hr in duration), they expressed mati ng ability 1.5 hr after the light pulse. Three wavelengths (416 nm, 54 7 nm, 626 nm) of light (5-sec pulse) were most effective for inducing the mating ability. Light pulses of more than 2 hr were sufficient to shift the phase of the circadian mating rhythm in DD, but phase shifts did not occur after light pulses of less than 1 hr. We obtained a pha se response curve (PRC) for light pulses of 6-hr duration. To investig ate the intracellular light-transduction pathway, we examined whether inositol triphosphate (IP3) could induce the mating activity in DD. Ce lls in the non-reactive phase of DD were injected with 10 pi of a solu tion of IP3 (120 mu M) under dim green light (480 nm, 8 mu W/cm(2)) wh ich did not induce mating ability. The cells begin to show mating acti vity 30 min after the injection and the extent of the activity was gre ater than that obtained by exposing cells to a 3 hr light pulse. Howev er, injection of IP3 did not cause phase shifting in DD. Thus, circadi an clock appeared not to be influenced by the injection of IP3. (C) 19 95 Wiley-Liss, Inc.