All Wound Up

Crawford Road (2), London, SE5

The recent white, drizzly atmosphere is giving me a real sense of being engulfed in the murky midsts of autumn. There’s a certain peacefulness to the air, as if the blank skies soften the soundscape; a deeply refreshing freshness too, and exotically colourful leaves at every turn. Strange as it might seem, I even feel excited about the impending dark afternoons. Darkness possesses its own intriguing allures that can almost give those heavenly long summer nights a run for their money. Almost!

In addition, I am provided with a seamless backdrop against which to view such spectacular structural delights as this: the helical winding of a branch demonstrating a perfectly executed slalom.

But then I go and ask myself the eternal question: How does it do it? How does it know where to go, when to turn?

I am happy because my questions have led me to the discovery of an excellent new word: thigmotropism. It sounds like a word made up by somebody who had forgotten the real word, a bit like thingamajig, but no, thigmotropism has real meaning. Thigmo in Greek means ‘touch’; tropism, also derived from a Greek word, refers to the biological phenomenon which occurs when an organism – usually a plant – grows or turns in a particular direction in response to an environmental stimulus, such as light, heat or gravity.

Or, as in this case, touch.

So, plants can feel! To be more specific, certain parts of certain plants, in particular the tendrils sent out by climbers to scout the nearby area for supporting structures, are exceedingly sensitive to what they touch. Their cells have tiny external bumps called tactile blebs (another wonderful word discovery) which are squashed out of shape by contact with another surface. Depending on the amount and direction of the squashing, the cell will know whether it has found a suitable support. Literally, within 30 seconds of touching an appropriate fence, coiling will begin.

Plants coil by two of two methods. The first happens really quickly and gets the ball rolling, whilst the second is a slower, more permanent response, solidifying the swivel. As soon as it has been decided that the tendril is now in contact with a suitable structure, the cells on the contact side of the stem lose water. This results in the contact side becoming softer and more malleable, whilst the non-contact side remains firm. This simple response forces a curve around the newly discovered support.

The second method occurs after about 24 hours, as long as the tendril has continued to receive contact stimulation from its fence. What happens, thanks to a complex series of events including the deployment of the plant hormone auxin, is that the cells on the non-contact side of the tendril actually grow faster, and therefore elongate more rapidly than those on the contact side. Result: plant growth in a permanent twirl.

What a brilliant solution! Of course the underlying biochemistry of the cell, how it communicates, regulates and implements all the necessary information is incredibly complex, but the physical manifestation of this biochemistry is so beautifully simple – grow one side of the stem at a faster rate than its opposite side and it can’t help but curl. Brilliant!

Oh dear. Now I can feel another question bubbling up! How and why, after twirling so elegantly for so many turns, did our hero decide that it had wound itself around quite far enough and that now was a good time to spread wide its branching network of life?

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  1. kininvie says:

    Lovely observation, Anna – and that’s two new words in my vocabulary too! I can’t answer your final question, but another springs to mind – how does a plant know that it has grown high enough?

    • anna says:

      Thanks Kininvie. That’s definitely another one to research. There are endless questions aren’t there! Do you mean when a plant reaches its final height and no longer grows any taller however old it is? Perhaps it’s age dependent – like us, we reach a maximum height at a certain age/point in our development. I’ve just read a pretty interesting book which you might enjoy – it’s about how plants sense their environment. It’s called:
      What A Plant Knows by Daniel Chamovitz

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