Plants in the fourth dimension( As anyone who has suffered from jetlag ...)

As anyone who has suffered from jetlag knows, we have internal clocks that tell us when to sleep and wake, and we can be miserable when these are disrupted. The daily cycles of many organisms are well known, but what has not been clear is whether these cycles are just responses to external cues of light, dark, heat, and cold, or if there are internal clocks that are set and reset by environmental signals. In animals, circadian rhythms are known to be important for maintaining a multitude of physiological processes. They may be even more critical for plants, which grow in many different light and temperature environments that not only vary with latitude but also with subtle differences within just a few feet. Plants respond to changes in light and temperature, opening flowers at dawn and closing them at night or blooming in the right season. However, they also have endogenous circadian ("around the day") rhythms with roughly 24 hour periods that are regulated by numerous genes that interact in complex pathways and cycles like exquisite 18th century clocks. These clock genes have been intensely investigated over the last 20 years, but we still do not fully understand the molecular mechanisms that make them run. Knowledge of these oscillations and the genes that regulate them could help us adjust the growth, development, and yield of crops under climatically variable conditions.

Dr. C. Robertson McClung and his colleagues are investigating the genetic basis and molecular mechanisms of circadian cycling and regulation in plants. Dr. McClung, of the Department of Biological Sciences, Dartmouth College, will be presenting this work at the President's symposium of the annual meeting of the American Society of Plant Biologists in Mrida, Mexico (July 1, 2:30 PM).

Clock genes have been identified in mammals, Drosophila, fungi, and cyanobacteria and their oscillatory mechanisms analyzed with studies of mutants. Many of these genes are c
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