by Igor Kulic on 11 September 2006
Despite their relatively sessile nature on macroscopic length scales plants are in fact quite motile on molecular and cellular level. They posses microtubules, actin filaments and corresponding molecular motors and use them to transport cargos through their cells pretty much in the same manner as animals do.
Interestingly plants (as animals) possess efficient motile organelles called axonemes that propel their sperm cells with a similar efficiency as in animals. Indeed plants feature all the basic components necessary to build muscles. So why did they “decide” not to follow this strategy? There is probably some deeper evolutionary mechanism behind this. My first guess: Muscle usage and maintenance requires a large energy throughput which might induce a supercritical entropy production in the environment if employed by every single species. This might render the whole ecosystem unstable.
Are plants indeed selfless evolutionary altruists dispensing with energetically expensive and aggressive muscle usage?
Of course we know of remarkable exceptions like the Venus flytrap not obeying the plant non-violence doctrine. The WMD of this rogue fellas seem to consist of an elaborate elasto-hydrodynamic system that generates a 100 msec super fast snapping of its “jaws”.
Another prominent way of moving in plant kingdom is hitchhiking. The essential philosophy behind is as simple as effective: Harness macroscopic fluctuations caused by other (motile) organisms to achieve motility without dissipating own energy. The list of hitchhiking plants is long and some of them are pretty stunning . In fact the Swiss engineer de Mestral was inspired by them to the extent that he came up with his Velcro mechanism. This was probably the first industrial bestseller driven by a truly biomimetic idea.
As kids we used to play with foxtail barleys (hordeum murinum). Although they belong to the same family of hitchhiker plants (as de Mestral’s Velcro muse Burdock) foxtail barleys are still exceptional. We used to put them between palms and by gently sliding our hands with respect to each other one could make the little green fella miraculously move uphill!
The origin of the underlying ratchet effect is interesting and is related to the geometric and elastic polarity of foxtail barleys surface structure.
I’ll post more on our foxy friend soon but here are already some appetizers (you need flash player >8 to view them):
1. Make a SEM journey on a foxtail barley hair and find out what makes it a ratchet.
2. See the barleys and other ratchet folks swirling around on a laboratory shaker. Note the strong directional component in their motion despite isotropic shaking.
To be continuedâ€¦