The Nature of Leaf Abscission

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Abstract
This review analyzes the various substances affecting leaf abscission, their possible mechanisms of action, and their relationship to the metabolism of senescent organs. Abscission is characterized by cell wall hydrolysis and separation of middle lamellae in an area known as the abscission zone. The pectic changes occurring in the separation area may be inhibited or stimulated by auxins, but the mechanism for these effects is unknown. The regulation of abscission appears to be by two systems, a restraint of abscission by auxin through a correlative action, and a provocation of abscission which may most likely be attributable to non-auxinic substances. Among these abscission stimulators are amino acids, ethylene gas, and apparently numerous other types of regulators yet to be identified.