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Biological Clocks "Wake Up" Plants

By David Elstein
April 2, 2003

Animal behavior has previously been shown to be shaped by 24-hour circadian rhythms that govern biological processes. Now scientists have found that these "biological clocks" exist in plants as well. Research at the Agricultural Research Service's Vegetable Laboratory in Beltsville, Md., has shown that a biological clock located in the nuclei of plant cells goes off every morning to prepare plants for their various activities.

"Circadian" is a Latin word meaning "about a day." Humans also have these rhythmic "clocks." Jet lag is an example of a person's biological clock being out of sync with the actual time of day.

ARS plant physiologist Autar K. Mattoo has found a few reasons why these inbuilt clocks go off every day in plants at precise times. He has spent considerable time specifically studying the one that controls an enzyme that modifies the protein known as D1, a critical element in the photosynthesis process.

Binding phosphorus to D1 at a specific threshold provides a plant with a bio-timing signal that tells it to adjust its metabolism to face the onset of the day's brightest light. The plant also puts on "sunscreen" to protect itself from ultraviolet-B (UV-B) radiation damage.

Experiments were conducted at different times of the year and in different climates, but the theory that the "alarm" goes off a few hours before noon almost always proved true. One thing that can block the accumulation of phosphorus on D1 is the concentration of triazine and urea-type herbicides, such as atrazine and diuron.

Mattoo worked on this project with researchers and students from the United States and Israel. As a result of their 22 years of collaborative research, these scientists were the first to determine the whole life cycle of the D1 protein.

More information about Mattoo's research can be found in the April issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.