leafabscission

Leaf abscission is the regulated shedding of leaves from a plant, typically occurring at a specialized region called the abscission zone (AZ) at the base of the leaf petiole. The process is an active, developmental program that allows the plant to remove leaves while protecting the exposed stem from infection and water loss.

Most leaf abscission involves coordinated hormonal and enzymatic changes. Ethylene generally promotes abscission, while auxin from the leaf blade inhibits AZ activation; a decline in auxin transport from the leaf often precedes abscission in response to seasonal cues or stress. In the AZ, cells undergo modifications that weaken adhesion to the surrounding tissues. Enzymes such as polygalacturonases, cellulases, and other cell-wall–degrading proteins break down the middle lamella and primary walls, enabling separation of leaf tissues. After detachment, a protective layer rich in suberin or lignin often forms on the exposed petiole stump to seal the wound and limit pathogen entry.

Triggers and timing of leaf abscission vary among species but commonly respond to environmental signals such as shorter day length, lower temperatures, drought, or mechanical stress, as well as developmental cues during autumn in temperate trees. Abscission can be seasonal, as in deciduous species, or induced by stress conditions.

Ecological and agricultural significance includes reducing water loss during drought, aiding seasonal energy budgeting, and facilitating harvest or crop management. Understanding leaf abscission informs breeding for stress tolerance, timing of harvests, and disease management in various crops.