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Even Plants Need to Sleep

Media Contact:
Jennifer Martin, CSREES Staff (202) 720-8188

August 13, 2007
By Stacy Kish, CSREES Staff

Sleep is an essential restorative practice for many organisms. Plants have developed a time-keeping mechanism, called a circadian clock, which allows them to anticipate daily changes in light and temperature. Scientists have now determined the plant's circadian clock controls its sensitivity to a hormone called auxin, which may result in a better understanding of plant responses to environmental change and stress, leading to optimized crop production.

The circadian clock plays a critical role in the temporal regulation of plant physiology, environmental responsiveness and development.  Plants coordinate growth and metabolism with respect to the time of day by producing self-sustained rhythms, which means that even without light and dark cues, circadian clock-controlled processes continue at the appropriate times over a 24 hour-period.

Auxin is a hormone that plays a critical role in regulating plant growth and development. This hormone also helps the plant orient itself properly in response to environmental cues such as light, gravity and water. For example, auxin allows the sunflower to follow the path of the sun through out the day. More than 70 years ago, researchers observed that plant sensitivity to auxin varied according to the time of day, but could not explain why this occurred, until now.

Using technology to look at the abundance of every gene product in an organism, Michael Covington and colleagues at the University of California?Davis determined that every step in the auxin-signaling pathway, from synthesis to response, is controlled by the plant circadian clock. The scientists showed that at different times of day, plants have a different sensitivity to auxin, controlling plant growth. This study demonstrates an intimate connection between the circadian clock and auxin-signaling pathways and suggests that other auxin-regulated processes may also be under circadian control.

Future work may elaborate on the connection between the circadian clock and auxin-mediated responses such as growth, development and environmental factors. This knowledge will allow scientists to better understand how plants cope with an ever-changing environment. Such knowledge will enable researchers to further optimize crop growth and development by both genetic and agricultural approaches.

This research is presented in the August issue of the journal Public Library of Science (PLOS) Biology.

The USDA's Cooperative State Research, Education, and Extension Service (CSREES) funded this research project through the National Research Initiative (NRI) Plant Biology program. NRI is the largest peer reviewed, competitive grants program in CSREES. It supports research, education and extension grants that address key problems of national, regional and multi-state importance in sustaining all components of agriculture.

CSREES advances knowledge for agriculture, the environment, human health and well-being, and communities by supporting research, education and extension programs in the Land-Grant University System and other partner organizations. For more information, visit http://www.csrees.usda.gov.

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