Blue light can reset the circadian clock in a wild-type strain of Chlamydomonas reinhardtii
Jennifer Forbes-Stovall and Sigrid Jacobshagen
Dept. of Biology, Western Kentucky University, 1906 College Heights Blvd #11080, Bowling Green, KY 42101-1080, USA
The circadian clock is an endogenous timer that oscillates with a period of approximately 24 hours and that is reset upon environmental time cues such as the daily light/dark or temperature cycles. Chlamydomonas reinhardtii is an ideal model organism for research on the circadian clock, because it shows several well-characterized behaviors that exhibit a circadian rhythm. Its circadian rhythm of phototaxis (swimming toward light) has been automated. Former action spectrum studies using the circadian phototaxis rhythm as an indicator surprisingly found that pulses of blue light were not effective in resetting the circadian clock of dark-adapted cells. This may have been because of the particular strain used in the study (the cell wall-deficient strain CW15). It may also have been due to the additional phase shift caused by the act of placing the cultures into the monitoring machine at particular times during their circadian cycle. This additional phase shift was most likely the result of the white background light present when monitoring the rhythm of phototaxis. We succeeded in improving the phototaxis monitoring process by using narrow-wavelength LEDs specific for phototaxis as our test lights and by omitting the background light between test light cycles. These modifications prevent any phase shifts due to the cultures being placed into the monitoring machine. Using our improved experimental set-up and the wild-type strain CC124, we now found that blue light is effective in resetting the circadian clock in Chlamydomonas reinhardtii.
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