Thigmotropism

Thigmotropism is a directional growth movement of curvature which occurs in response to stimulus of contact. Thigmotropism is found in twiners and tendrils. After initial contact with support due to nutation, the tendril or twiner shows less growth in the region of contact and more growth on the other side. As a result they bend over the support. Later on bending or coiling may occur in lower parts of the tendril as well. Thigmotropism is a movement in which a plant moves or grows in response to touch or contact stimuli. The prefix thigmo- comes from the Greek for "touch" (θιγμός). Usually thigmotropism occurs when plants grow around a surface, such as a wall, pot, or trellis. Climbing plants, such as vines, develop tendrils that coil around supporting objects. Touched cells produce auxin and transport it to untouched cells. Some untouched cells will then elongate faster so cell growth bends around the object. Some seedlings also exhibit triple response, caused by pulses of ethylene which cause the stem to thicken (grow slower and stronger) and curve to start growing horizontally.