Auxin and Early Stages of the Abscission Process of Citrus Leaf Explants

The petiole-leaf blade abscission zone in citrus is surrounded by a notch. The cells at the base of the notch double or triple in size during the first hours after excision, and this cell enlargement is correlated with an increase in endogenous auxin in the abscission zone. At a later stage, the level of auxin decreases, as does the ability of auxin to induce H+ efflux or to bind specifically to a particulate membrane fraction from the abscission zone. We suggest that the decrease in the ability of auxin to delay abscission at a later stage of the abscission process is connected with the decrease in the ability of receptor proteins to bind auxin. However, the decrease in auxin-induced H+ efflux is correlated with, but not necessarily causally related to, abscission.