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This article is part of the supplement: IUFRO Tree Biotechnology Conference 2011: From Genomes to Integration and Delivery

Open Access Oral presentation

Dual function of auxin during leaf abscission in poplar

Xu Jin12* and Urs Fischer12

  • * Corresponding author: Xu Jin

Author Affiliations

1 Swedish Agricultural University, Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Umeå, Sweden

2 University of Göttingen, Forest Botany and Tree Physiology, Göttingen, Germany

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BMC Proceedings 2011, 5(Suppl 7):O26  doi:10.1186/1753-6561-5-S7-O26

The electronic version of this article is the complete one and can be found online at:

Published:13 September 2011

© 2011 Jin and Fischer; licensee BioMed Central Ltd.

This is an open access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Leaf abscission is an important trait for biomass production and seasonal acclimation in deciduous trees of the temperate region. Various plant hormones are involved in the timing of abscission. For example, ethylene signaling is required to induce hydrolysis of cell walls, while an auxin gradient [1] was suggested to act upstream of ethylene on the onset of leaf abscission. Besides pharmacological application of auxins on cut surfaces of explants, experimental evidence for such a gradient is however lacking. In addition to its function in temporal control, auxin has also been suggested to be a positional signal specifying the cells of the abscission zone [2].


We established an experimental system on intact Populus trees, which allows us to induce abscission synchronously under controlled conditions. Leaf blades were bagged in aluminum foil and abscission was recorded daily. Cumulative abscission followed a sigmoidal curve for dark-induced leaves, whereas control leaves in transparent bags of the same weight as the aluminum foil bags were not separated from the stem. Abscission was preceded by senescence in the petiole but not in the leaf.

Results and conclusions

Local auxin applications directly onto the abscission zone, as well as onto the distal end of the petiole, delayed dark induced abscission indicating that auxin could range not only as a short but also as a long distance signal. Similarly, an inhibitor of polar auxin transport retarded separation from the plant body. By contrast, auxin applied onto mature abscission zones only delayed abscission slightly in comparison to auxin applications before the development of an abscission zone. Taken together this points to a distinct function of auxin in early stages of abscission. Interestingly, we found shortly after dark-induction a new auxin response maximum on the abaxial side of the petiole, highlighting the incipient abscission zone. This auxin response maximum progressively moved from the abaxial to the adaxial side of the petiole, preceding the maturation of the abscission zone, presumably providing positional information for the formation of the abscission zone. Microarray data identified the auxin efflux carriers PIN1 and PIN5, as well as a novel auxin transporter, to be down-regulated after dark induction. Immunolocalizations of those carriers will reveal if their subcellular localization and expression can explain the novel auxin response maximum.


  1. Louie DS, Addicott FT: Applied auxin gradients and abscissin in explants.

    Plant Physiology 1970, 45(6):654-658. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  2. McManus MT, Thompson DS, Merriman C, Lyne L, Osborne DJ: Transdifferentiation of mature cortical cells to functional abscission cells in bean.

    Plant Physiology 1998, 116(3):891-899. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL