epinasty

Epinasty is a plant growth response in which a leaf, petiole, or other organ bends downward as a result of asymmetric growth on opposite sides. The curvature occurs when tissue on one side elongates more than tissue on the opposite side, causing the organ to droop or point downward.

The effect is often associated with hormonal signaling, especially ethylene. Ethylene production or sensitivity can promote differential growth, leading to downward bending. Epinasty can also be influenced by other factors such as aging, mechanical stimulation, drought, wounding, or environmental stress, which disturb the balance of growth regulators and tissue expansion.

Common occurrences include leaf and petiole epinasty, and it is frequently observed during fruit ripening in species like tomatoes and cucumbers. In horticulture and postharvest handling, epinastic movements can affect leaf orientation, light interception, and crop quality, making awareness of this response relevant for crop management.

Epinasty is contrasted with hyponasty, the upward bending of plant organs brought about by different growth patterns or environmental cues. Understanding epinasty helps illuminate how plants modulate organ orientation in response to internal signals and external conditions, contributing to studies of plant physiology, development, and crop performance.