EMBARGOED UNTIL

THURS., FEB. 23, 1995



RESEARCHERS SHED LIGHT ON THE BIOLOGICAL CLOCKS OF PLANTS

	CHARLOTTESVILLE, Va., Feb. 23 -- Using plants genetically
engineered to glow in the dark, researchers at the NSF Center for
Biological Timing have produced plants that have altered circadian
rhythms.  These mutant plants provide the first significant
breakthrough towards understanding the mysterious biological clocks
that control many important plant functions, from photosynthesis to
determining when to flower and set seed.  This fundamental research
into how plants tell time may have future applications in
agriculture, such as the ability to manipulate the time of
flowering, say the scientists.
	In a pair of papers scheduled to appear tomorrow in the
journal Science, University of Virginia biologist Steve A. Kay and
his colleagues describe their research with Arabidopsis, a small
plant related to mustard that is ideally suited for laboratory
studies.  Green plants use light as a source of energy, as a signal
to flower, and as a cue for controlling their growth and
development.  Plants have a variety of photoreceptors to detect
changes in both the amount, color and direction of the sunÕs rays.
	Plants, like other creatures ranging from fruit flies to
humans, have innate cycles of activity that last about a day and are
called circadian rhythms.  Currently, little is known about the
molecular ÒcogsÓ that run these biological clocks.  By comparing
mutant organisms with altered circadian rhythms to their normal
counterparts, researchers can eventually track down and uncover
these elusive clock molecules.
	In 1992, Kay, working with Andrew Millar, a graduate student
from Rockefeller University, developed an experimental system in
which luciferase, the gene that enables fireflies to glow, was
inserted into Arabidopsis plants.  The luciferase gene was linked to
a plant gene called CAB, which gets switched on in the morning and
off in the evening.  Whenever the CAB gene is activated, the
luciferase gene is also turned on and the plants glow the same
yellow-green color as fireflies.  This clever genetic trick enabled
the researchers to follow the rhythms of individual plants by
measuring their glow using highly sensitive video cameras.  In this
way they were able to identify mutant plants in which the biological
clock is running either too slow or too fast.  One of these mutant
genes, called toc1, makes several different rhythms too short .
ÒThis means it must be something central to the timekeeping
mechanism of the plant,Ó says Kay.
	One common aspect of circadian clocks in all organisms is
that they need to be Òreset,Ó or wound up by light each day.  Kay
and his colleagues have been able to use their glowing plants to
understand how the light signals reach the clock.  By studying how
the glow rhythm behaves in mutant plants that were either blind to
specific colors of light, or were fooled into thinking light was
present in the dark, the researchers showed that both red and blue
light could alter the tempo of the plant clock.  ÒIt is very
important for the plant to be exquisitely tuned to its environment,Ó
says Kay, Òand now we can begin to unravel how the plant uses its
clock, along with its photoreceptors, to tell what time dawn and
dusk occurred.Ó In this way plants are able to tell if the days are
getting longer or shorter, and therefore decide when best to flower.
###  
February 22, 1995
FOR MORE INFORMATION, call Dr. Steve Kay at (804) 924-0698.