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DEVELOPMENT AND HORMONE ACTION

Circadian Timekeeping during Early Arabidopsis Development^1,[W],[OA]

Dartmouth College, Department of Biological Sciences, Hanover, New Hampshire 03755–3576

The circadian coordination of organismal biology with the local temporal environment has consequences for fitness that may become manifest early in development. We directly explored the development of the Arabidopsis (Arabidopsis thaliana) clock in germinating seedlings by monitoring expression of clock genes. Clock function is detected within 2 d of imbibition (hydration of the dried seed). Imbibition is sufficient to synchronize individuals in a population in the absence of entraining cycles of light-dark or temperature, although light-dark and temperature cycles accelerate the appearance of rhythmicity and improve synchrony among individuals. Oscillations seen during the first 2 d following imbibition are dependent on the clock genes LATE ELONGATED HYPOCOTYL, TIMING OF CAB EXPRESSION1, ZEITLUPE, GIGANTEA, PSEUDO-RESPONSE REGULATOR7 (PRR7), and PRR9, although later circadian oscillations develop in mutants defective in each of these genes. In contrast to circadian rhythmicity, which developed under all conditions, amplitude was the only circadian parameter that demonstrated a clear response to the light environment; clock amplitude is low in the dark and high in the light. A circadian clock entrainable by temperature cycles in germinating etiolated seedlings may synchronize the buried seedling with the local daily cycles before emergence from the soil and exposure to light.

² Present address: Max Planck Institute for Developmental Biology, Department of Molecular Biology, Spemannstrasse 37–39, D–72076 Tübingen, Germany.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: C. Robertson McClung (mcclung{at}dartmouth.edu).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.117622

^* Corresponding author; e-mail mcclung{at}dartmouth.edu.

Received February 25, 2008; accepted May 11, 2008; published May 14, 2008.

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