Every year little blue flowers emerge…I can never remember their name and always have to ask Mrs Sciencebase to remind me…oh yeah: “forget-me-not” also known as “mouse’s ear” because of the shape of its leaves, and one of many types of scorpion grass, common one here has the scientific name Myosotis scorpioides)
But, the forget-me-not is not the only plant giving us orders, there’s also the “touch-me-not” (Mimosa pudica, the shame plant; pudica is Latin for shy, bashful or shrinking (as in violet)) Anyway, the pinnate leaves of this species will fold back on to themselves quite quickly with the gentlest touch.
This behaviour is presumably a protective mechanism to avoid the leaves being eaten by herbivorous insects or to make it awkward for female insects to lay eggs on the surface of the leaves. So, how does a plant “know” to do this with its leaves? The leaves of many plants respond to changes in light and weather by closing up, it is known as seismonastic movement, most are quite slow, but all involve plant chemistry responding to an external stimulus whether falling light levels, temperature change, wind or the touch of a finger (or insect alighting on the leaf).
Whatever the stimulus it is transmitted through electrochemical changes at the cellular level, passage of an action potential which causes potassium ions to flow out openings in the plant cell walls, this then causes water to flow out of the cells through osmosis through the cells aquaporin channels, to attempt to balance the change in potassium ion concentration. Loss of water from the cells makes them floppy, or technically speaking become less turgid. Differences in turgidity in different regions of the leaf and stem lead to the “closing” of the leaflets.