The effects of blue and red light on Acetabularia mediterranea after a long dark period: recovery of the endogenous rhythms of transcellular electrical potential and chloroplast velocity

Abstract

After a long dark period (2 – 8 weeks), the transcellular electrical potential along the cell of Acetabularia mediterranea has almost disappeared and cytoplasmic streaming is at a stop. Irradiation with continuous blue light (450 nm) induces the transcellular electrical potential to increase and oscillate. After two shorter oscillations, the rhythm becomes firmly established with a period around 23 h. This behaviour is similar to that observed in white light, where the final period is around 26 h. White light and blue light induce the appearance of endogenous diurnal oscillations in the velocity of the cytoplasmic streaming which resumes following a periodicity pattern similar to that of the transcellular electrical potential. Irradiation with continuous red light (650 nm) causes a strong increase of transcellular electrical potential and recovery of cytoplasmic streaming but seldom induces these two processes to resume with the typical oscillations. However, after irradiation with blue light, the rhythm of transcellular electrical potential persists for some time in red light but disappears progressively. When blue light is given after red light, the transcellular electrical potential rhythm resumes immediately. Blue light may be considered as a "Zeitgeber."