title: Auxin is a long-range signal that acts independently of ethylene signaling on leaf abscission in Populus.
abstract: Timing of leaf abscission is an important trait for biomass production and seasonal acclimation in deciduous trees. The signaling leading to organ separation, from the external cue (decreasing photoperiod) to ethylene-regulated hydrolysis of the middle lamellae in the abscission zone, is only poorly understood. Data from annual species indicate that the formation of an auxin gradient spanning the abscission zone regulates the timing of abscission. We established an experimental system in Populus to induce leaf shedding synchronously under controlled greenhouse conditions in order to test the function of auxin in leaf abscission. Here, we show that exogenous auxin delayed abscission of dark-induced leaves over short and long distances and that a new auxin response maximum preceded the formation of an abscission zone. Several auxin transporters were down-regulated during abscission and inhibition of polar auxin transport delayed leaf shedding. Ethylene signaling was not involved in the regulation of these auxin transporters and in the formation of an abscission zone, but was required for the expression of hydrolytic enzymes associated with cell separation. Since exogenous auxin delayed abscission in absence of ethylene signaling auxin likely acts independently of ethylene signaling on cell separation.
authors: Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural Sciences Umeå, Sweden ; Forest Botany and Tree Physiology, Georg-August University of Göttingen Göttingen, Germany.
authors: Xu
authors: X
authors: Jin
authors: Forest Botany and Tree Physiology, Georg-August University of Göttingen Göttingen, Germany.
authors: Jorma
authors: J
authors: Zimmermann
authors: Forest Botany and Tree Physiology, Georg-August University of Göttingen Göttingen, Germany.
authors: Andrea
authors: A
authors: Polle
authors: Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural Sciences Umeå, Sweden ; Forest Botany and Tree Physiology, Georg-August University of Göttingen Göttingen, Germany.
authors: Urs
authors: U
authors: Fischer
keywords: PIN proteins; Populus; abscission; auxin; cell separation; ethylene