abscission

Abscission is the process by which a plant organ, such as a leaf, fruit, flower, or seed, is shed from the plant. In most plants this shedding occurs at specialized positions called abscission zones (AZs) located at the base of the organ. The AZ comprises a group of cells that form a separation layer capable of weakening adhesion with the surrounding tissue while the rest of the plant remains intact.

The detachment results from the coordinated degradation of cell walls and the middle lamella within the separation layer. Enzymes such as cellulases, polygalacturonases, and pectin esterases break down cell wall components, allowing cells to separate. Changes in turgor pressure and the dissolution of adhesive substances further facilitate detachment. Ethylene is a key promoter of abscission, while auxin from the adjacent tissues generally inhibits AZ sensitivity. When auxin levels decline—due to maturation, aging, or wounding—the AZ becomes more responsive to ethylene and abscission proceeds.

Environmental and developmental triggers influence abscission. These include seasonal changes, drought, nutrient status, light conditions, and physical damage. Hormonal balance, particularly between ethylene and auxin, governs the timing and extent of shedding, sometimes in response to damage or pathogen pressure.

Ecological and practical significance is notable. Abscission enables fruit and seed dispersal, reduces resource load, and aids seasonal adaptation. In agriculture and horticulture, abscission can be managed to optimize harvest timing, improve thinning, or control postharvest drop through the use of hormones or inhibitors.