"Clocks are adaptive; they contribute to the fitness of an organism in any particular environment," says McClung. "We found that in species like Arabidopsis, which cover a huge environmental range, there are underlying variations in their circadian clocks to subtly optimize their ability to function in a particular environment."
Published in the November 7 issue of Science, the study examines the clock rhythms in Arabidopsis from different parts of the earth. The researchers analyzed leaf movements and measured the period of time it took the leaves to complete one circadian cycle, noted the time of day when the leaves were pointing straight upward, and calculated the distance the leaves moved during a cycle. All three measurements showed considerable differences in the plants from different areas.
"When we determined day length in each of the latitudes for the plants, we found the correlation was highly significant between the circadian variations in period length and the latitudes of origin of the different plants," says McClung.
A second component of the study provides evidence suggesting that a large number of genes contribute to fine-tuning the Arabidopsis clock.
By crossing Arabidopsis from two different geographic areas, and allowing them to segregate for a number of generations, the researchers identified five chromosomal regions, called quantitative trait loci (QTL), which significantly contribute to either period length or phase or amplitude of the rhythms. Each of these QTL regions includes many genes, at least one of which con
Contact: Sue Knapp