Time for flowers

Scientists are catching up with the biological clock in plants

Published: Sunday 30 April 1995

-- (Credit: Rustam Vania)JET-lagged globetrotters are familiar with that peculiar urge to sleep when they should be wide awake, and vice versa. They'll blame casually it on a biological clock shot to bits by all their indiscriminate peregrinations. But the biological clock is no minor functionary: it is the "internal timekeeper" of our physical destinies. Even plants have it ticking away inside, controlling processes like leaf movements to facilitate optimum absorption of light.

What is mysterious is the way the clock is set and reset in plants. It may, however, soon be possible to crack the puzzle with the help of the research findings of some American scientists. One notable success in recent years has been the identification and cloning of clock-related genes in mice, hamsters and cyanobacteria, which could provide insights into how the tickers actually work.

So far, plants have refused to give up the secret. Researchers are unable to pinpoint mutant plants with defective biological clocks or abnormal rhythms, from which such genes could be isolated. This problem has now been tackled by a research team led by Steve Kay of the University of Virginia, which identified some genetic mutations that alter the internal clocks of tiny laboratory plants called Arabidopsis (Science, Vol 276 No 5201)

Kay and his colleagues began with the dna sequences from a clock-regulated Arabidopsis gene, chlorophyll-a/b-binding (CAB) proteins. CAB is normally activated during the day, remaining passive at night, and maintains this rhythm, directed by the plant's internal clock. The Virginia team attached the regulatory dna sequences to a firefly gene which produces an enzyme that causes a chemical called luciferin to glow. When sprayed with luciferin, plants carrying the engineered luciferase gene glowed only during the day. "This has made the search for clock mutant plants very simple: just look for seedlings that glow at the wrong time," exclaims Kay.

Using this technique developed by Kay, Andrew J Millar from the National Science Foundation Centre (NSF) for Biological Timing, Department of Biology, University of Virginia, and his colleagues identified mutant Aradopsis seedlings with rhythms ranging from 21-28 hours.

Although the team has not yet determined the altered genes responsible for the changed rhythms, Miller hopes that the ingenuity of the method and the potential of the mutants letting the cat out will help to finally crack the mystery.

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