Time-course showing the circadian rhythm of bioluminescence in a population of Arabidopsis thaliana seedlings expressing the firefly luciferase gene under the control of the Arabidopsis CAB2 promoter. The time-course follows the rhythm of transcription from the CAB2 promoter over 48 hours. Two circular 10 cm petri dishes of seedlings are represented for each time-point. Twenty-five images are shown, taken at 2 hourly intervals over the course of 2 days and should be followed as if reading a book, from left to right, one line at a time.

The seedlings, germinated on growth medium were first entrained 12 hour light/12 hour dark cycles for 6 days then transferred to constant light. The sequence commences during the morning of the first day after transfer to constant light. The CAB2 gene encodes part of the photosynthetic machinery and appropriately shows a peak of expression during the subjective day and a trough of expression during the subjective night. Images were taken using a NightOwl cooled CCD camera.