How do abscisic acid and ethylene influence leaf fall and plant dormancy?

Abscisic acid and ethylene are key plant hormones that function as growth inhibitors, playing significant roles in regulating leaf abscission and the onset of dormancy.

Leaf Abscission

Leaf fall is a complex process involving the formation of an abscission layer at the base of the petiole. While auxins generally retard this process, ethylene and abscisic acid promote it:
* Ethylene: This hormone plays a significant role in leaf abscission by stimulating the synthesis of enzymes that catalyze the breakdown of cell walls in the abscission zone.12
* Abscisic Acid: This hormone accelerates the senescence associated with leaf fall, though its specific role in the abscission process itself remains a subject of scientific debate.12

Plant Dormancy

Both hormones are instrumental in helping plants survive unfavorable environmental conditions, such as winter or drought:
* Abscisic Acid: Often referred to as a dormancy hormone, it promotes the development of resting buds in woody plants and induces stomatal closure during water stress.12
* Dormancy Regulation: The transition into winter dormancy is often triggered by environmental signals like shortening day length, which leads to the formation of inhibitor compounds. The resumption of growth in the spring typically involves a shift in the balance between growth-inhibiting substances like abscisic acid and growth-promoting hormones such as gibberellins.2