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Pulsating plants
by David Catchpoole
Plants never cease to amaze the researchers who study our planet’s greenery.
With every new impressive discovery about the complex workings of plants,1,2
the more we realize how little we know about them.
This is especially so in relation to roots, which, being underground, have traditionally
been more difficult to study than above-ground parts (leaves, stems and flowers).
However, with improved technology, the mysteries of root growth are slowly coming
to light.
For example, using sophisticated video imaging techniques, a research team led by
University of Wisconsin botanist Simon Gilroy has been able to view the growth of
delicate extensions of individual root cells, known as root hairs.3
There are literally millions of these elongated skinny projections covering plant
roots. It’s long been realised that root hairs hugely increase the surface
area of plant root systems, thus increasing the volume of soil from which water
and mineral nutrients can be obtained by the plant. But precisely how root hairs
form and grow has remained a mystery.
To Gilroy and his team’s surprise, when they trained their cameras on the
hairs, they did not witness the slow, steady lengthening they had expected. Instead,
they saw the root hairs undergoing rhythmic pulses of growth every 20 seconds or
so. Further investigation linked the pulses to rapid changes in pH (acidity/alkalinity)
at the root hair tip and also to the levels of certain reactive chemical compounds.
Plants are not slow or static, but far more complex and sophisticated than imagined
The findings show that plants are not slow or static, but far more complex and sophisticated
than imagined.
“Plants are actually much more dynamic than you’d think by looking at
them just sitting there, soaking up the sun,” Gilroy says.4 In fact, plants are responding to cues on timescales
of seconds to milliseconds—a rapidity usually associated only with animal
responses.
What’s more, as Gilroy explained, unlike animal cells, enlarging plant cells
have to contend with a cell wall made of cellulose, which is, weight for weight,
stronger than steel. The reinforcing strength of cellulose stops the cell bursting
from the tremendous water pressure (turgor) inside. But for the tip of the root
hair to grow, the cell must somehow make the cell wall there just flexible enough
to stretch from the internal pressure without bursting. It must then quickly strengthen
the wall directly behind the tip once extension has occurred.
How on earth does a plant cell do this?—Botanist Simon Gilroy
“The plant cell has to work out where to make the wall stiff, where to make
it loose, and control this so finely that the turgor pressure doesn’t absolutely
shoot the end off the cell and kill it,” says Gilroy. “It’s always
been a conundrum: How on earth does a plant cell do this?”
Gilroy and his colleagues had thought that perhaps the plant cell carefully pumps
protons into the cell wall to create a gradient of acidity, resulting in steady
elongation of the root hair. But, as already mentioned, they saw pulsating
growth, which was indeed mediated by protons but in a much livelier manner than
expected.
When protons flow into the cell wall, the wall stretches and the root tip lengthens—but
the plant cell sucks protons back out again almost immediately, and the
cellulose strands lock in place to strengthen the cell wall again. After a brief
pause, the cycle is repeated.
Why these growth pulses instead of steady elongation? Gilroy suspects that because
the root hair is at such risk from weakening the wall too much and bursting, it
takes a quick “breather” to check on things. “There’s a
lot of regulation invested in slowing things down and waiting to see if the cell
is okay, before going on,” he explains.
The chemical regulation of these pulses is highly complex, and Gilroy acknowledges
there is much more about it that is still unknown. “Everything’s coordinated.
It’s like a dance,” he says, with the entire complicated ballet occurring
up to three times per minute.
Just as every great ballet needed a choreographer, so too this “entire complicated
ballet” that’s been going on repeatedly in the ground under our feet
for years, without our even being aware of it, must have been choreographed. The
Bible tells us just who that Choreographer is (Psalm 104:14, 1 Corinthians 3:7).
References
- Scientists admit they have much more yet to learn about the
plant’s inner workings. For example, the intricate complexity of the chemistry
behind photosynthesis—the conversion of sunlight into usable energy—which
bioengineers are eager to copy. See: Can we make “green energy” as plants
do? Creation 31(3):8, 2009. Return to text.
- Even the more visible exterior parts such as flowers continue
to reveal hitherto unrealized features. High-speed video cameras recently showed
the bunchberry’s pollen catapult (designed like a medieval trebuchet) to be
the fastest natural catapult yet discovered. Catchpoole, D., Bunchberry bang! Creation
31(2):32–34, 2009; creation.com/bunchberry. Return
to text.
- Monshausen, G., Bibikova, T., Messerli, M., Shi, C. and Gilroy,
S., Oscillations in extracellular pH and reactive oxygen species modulate tip growth
of Arabidopsis root hairs, Proceedings of the National Academy of Sciences USA
104(52):20996–21001, 26 December 2007. Return to text.
- Fisher, M., What lies beneath: Growth of root cells
remarkably dynamic, study finds, University of Wisconsin news release, <www.news.wisc.edu/14505>,
3 December 2007. Return to text.
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