thigmotropi

Thigmotropism is a directional growth response of organisms, especially plants, to touch or physical contact. In plants it is most noticeable in climbing species and tendrils, where growth occurs toward a support (positive thigmotropism) or away from a touching surface (negative thigmotropism). While shoots commonly exhibit positive thigmotropism by curling around objects, roots can also display thigmotropic responses as they encounter obstacles.

The mechanism involves the perception of mechanical stimuli by specialized receptors, followed by signaling cascades that alter growth patterns. Calcium signaling, changes in cell turgor, and hormonal redistribution—particularly of auxin—produce differential growth on opposite sides of the touched organ. The result is bending or coiling toward or away from the contact point. Thigmotropism interacts with other growth responses such as gravitropism and phototropism, and is part of a broader set of mechanosensitive adaptations in plants.

Common examples include tendrils of climbing plants curling around supports, stems bending toward a contact surface, and some roots adjusting their path to navigate around obstacles. In addition to plants, thigmotropic-like responses have been noted in certain fungi and other sessile organisms, where contact with a surface guides growth direction.

Historically, the concept has been studied since the 19th century as part of plant tropism research. The term derives from Greek thigmos, touch, and trope, turning. Thigmotropism remains a key example of how mechanical stimuli influence plant morphology and ecology.