Posted on homepage: 15 February 2010 (GMT+10)
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.
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.
“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).
- 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.