JELLYFISH-TOBACCO GENE COMBO. REVEALS BIO
By Sean Henahan, Access Excellence
An unusual bit of genetic engineering involving luminescent
jellyfish and tobacco plants has revealed a key role for calcium
in biological rhythms, report researchers at Vanderbilt
Calcium is known to regulate numerous intercellular events such
as glucose metabolism, muscle contraction and ion movements in
the brain. In an attempt to discover the role of calcium in
circadian plant rhythms the researchers created a transgenic
plant in which a gene from glow-in-the-dark jellyfish was
transported into tobacco cells. The enzyme made from this gene
emits light only when calcium is present, allowing the
investigators to monitor calcium levels in the tobacco cells by
tracking the amount of light emitted.
Lead investigator Carl Johnson, an associate professor of
biology at Vanderbilt, had been conducting experiments with
calcium for more than ten years. However, his previous
experiments were unsuccessful because the techniques available
to measure calcium at the time weren't conducive to long-term
recordings. To adequately study biological rhythms, experiments
must last at least several days at a time. The genetic
engineering experiments allowed him to at last conduct longer
term experiments, in this case averaging eight days.
"For the first time, we were able to examine the role the
circadian clock plays in regulating calcium," Johnson said.
"This, in turn, might explain how the clock controls all
different kinds of observable rhythms that impact our lives."
Evaluated calcium transport in plant cells, tissues and
seedlings. Luminescence testing showed a correlation between
cytosolic calcium concentrations and circadian rhythms, with
peak levels seen immediately after dawn. The researchers were
able to shift the luminescence rhythm by extending the darkness
interval in the light-dark cycle.
Plants have very complex circadian rhythms which involve, among
other things, the movements of stems, petioles and stomatal
apertures. All of these process are known to respond to turgor
pressure which is itself regulated by potassium and calcium
ions. Calcium also regulates such key process as growth and
mitosis, protein kinases and gene expression of chlorophyll
binding proteins, he said.
The current research suggests a mechanism linking calcium and
plant biorhythms in processes including the timing of growth and
flowering, plant movement and gene expression it also suggests
that calcium is regulated differently in distinct compartments
of the plant, he noted.
In nature, the circadian system stimulates processes such as
flowering, animal reproduction and migration, Johnson said. For
example plants annually flower in the spring and make seeds in
the winter. The circadian clock is the timer they use to measure
the day and night length that triggers this rhythm.
"I'm hoping that ultimately these studies on plant genes and on
calcium's link to the circadian clock will reveal exactly how
the clock works," said Johnson, adding it's likely that daily
clocks drive seasonal clocks. Chronobiologist can then search
for molecular mechanisms that answer questions such as what
makes deer breed in the spring and human immune systems beef up
their defenses in winter.
"Biological rhythms govern everything from alertness and sleep
to body temperature and hormone production," Johnson said. "As
chronobiologists we try and help people better understand jet
lag, winter depression, adjusting to shift work, disrupted sleep
patterns, accidents due to drowsiness and the optimal time of
day to administer drugs."
Physicians have found that the course of diseases can change in
daily cycles. Heart attacks, joint pain and migraine headaches
are more likely to occur in the morning, for reasons that are
not entirely clear. Johnson is one of few chronobiologists to
teach medical students about circadian rhythms.
The Vanderbilt study appeared in Science, Vol. 269., Sept.
Related information at other
Ag. BioTech Links