I’ve just been down to my allotment and picked some runner beans (just in case 'runner bean means something else where you are, I’m talking about this)
I noticed that the plants are twining around/up the canes in an anticlockwise direction, the reverse of what I would expect if the twining was simply a case of the motile shoot following the sun, but then I think that runner beans originate in the southern hemisphere.
Is this right? do (native)nothern-hemisphere climbers tend to twine in a clockwise direction and vice versa?
I have tried training shoots in the wrong direction; they tend to either revert to twining in an anticlockwise direction, or they actually ‘unwind’ themselves and fall off the cane.
BTW, we’re talking about a row of maybe 100 plants of a mixture of three varieties and every one is twining this way, so I think there’s obviously something going on…
I’m asking because I remember seeing time-lapse films of growing plants and the growing points always seem to follow the sun (gyrating in a clockwise pattern in the nothern hemisphere) - I’d always thought that this would automatically prejudice climbing plants to a clockwise spiral path, but (with runner beans at least) this is not the case; made me wonder of the behaviour became ‘built-in’ at some point.
I’m not talking about the coriolis effect, which is all about forces caused by the rotattion of the earth, I’m talking about the [apparent]motion of the sun across the sky.
Interestingly Hops (Humulus Lupulus), which twine clockwise) are native to the northern hemisphere, kidney beans, which are native to the southern hemisphere twine anticlockwise. So far, this supports my hypothesis. The article that you posted mentions Darwin’s experiments with climbers which didn’t have a preference for twining direction, for the purposes of this discussion, I feel we must exclude species which show no definite and consistent behaviour and confine ourselves to those which always twine in the same direction. (I now shan’t be too surprised if I learn that some of the plants with no preference for twining direction originate in the tropics)
Now the article says that kidney beans always twine anti-clockwise, wherever grown, and this is my initial observation (I am growing them in the northern hemisphere)
My question really is whether the twining behaviour of climbing plants might originally have been a simple case of the growing shoot tracking the sun, but over time, the twining direction became inherited, rather than simply behavioural (I’m not suggesting that something got ‘written back’ to the plant’s genome - there are a couple of threads going about this subject already - I’m suggesting that maybe the plants that (through some mutation or other) inherently twined in the direction that follows the sun might have some advantage over their cousins that don’t.
IIRC from my biology classes, oh so many years ago, plants exhibit tropic and nastic responses. A tropic response is one which relates to the direction of some stimuli such as phototropism where the plant grows towards a light source. What you describe with the bean plants is however a nastic response and does not relate to the directionality of any stimuli. They grow like that to wind around any supporting structure, not to catch more light.
NO! - perhaps I should put it this way; suppose there are two populations of closely related twining climbers, both derived from a common ancestor with no particular preference for direction of spiralling, some completely random mutation has disposed one population to twine in a direction that follows the sun, the other in the opposite direction (OK, I know that two such mutations at the same time would be unlikely, but stay with me) - suppose twining in the same direction as the sun’s travel confers the tiniest advantage (or twining in the opposite direction confers a tiny disadvantage); the mutant with the advantage is going to win out in the end.
but actually that’s not strictly tropic behaviour turning into inherited behaviour I suppose (it’s too easy to look at those time-lapse films of gyrating seedlings and imagine that this is the only possible origin of twining behaviour); I should rework my question, thus;
Is there any significant statistical correlation between the direction of twining (of plants that show a marked and consistent preference, despite where they are grown) and their hemisphere of origin?
Twining (or more generally, circumnutation) chirality is indeed genetic. Witness this mutant left-handed Arabidopsis plant.
Marinelli, B et al. 1997. A pleiotropic Arabidopsis thaliana mutant with inverted root chirality. Planta 202:196-205.
The mechanism described by Mangetout sound plausible, but I can’t find any data correlating handedness to geography. Note that the abstract says that most plants are right-handed.
