© 2007 Heron Publishing—Victoria, Canada
Exudation of organic acid anions from poplar roots after exposure to Al, Cu and Zn
Ruijun Qin (1), Yasuhiro Hirano (1, 2) and Ivano Brunner (1, 3)
1. Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), CH-8903 Birmensdorf, Switzerland / 2. Kansai Research Center, Forestry and Forest Products Research Institute (FFPRI), Kyoto 612-0855, Japan / 3. Corresponding author (ivano.brunner@wsl.ch) / Received January 5, 2006; accepted March 4, 2006; published online November 1, 2006
Summary
We studied the effects of a 2-day exposure to aluminum (Al), copper (Cu) and zinc (Zn) stress on root exudates and root apices
of aseptically grown poplar (Populus tremula L.) cuttings. Aluminum induced root exudation of oxalate and citrate, Cu induced root exudation of oxalate, malate and formate,
and Zn induced root exudation of formate. The threshold treatment concentrations were 100 µM for Cu and 500 µM for Al and
Zn, corresponding to about 30 µM Cu2+, 140 µM Al3+ and 290 µM Zn2+. Simultaneous with the increase in organic acid anion exudation, sulfate and the nutrient cations K+, Ca2+ and Mg2+ were released into the solutions. Significant positive correlations between the organic acid anions and the cations indicate
possible co-release. Toxicity symptoms of the poplar roots included browning of the root apices, which occurred at Cu concentrations
of 50 µM and above, at Zn concentrations of 500 µM and above, and at an Al concentration of 1000 µM, and callose formation,
which was observed solely in response to Al concentrations of 500 µM or higher. The results indicate that the composition
of the exuded organic acid anions from poplar roots and the toxicity symptoms are specific to each of the applied heavy metals.
Keywords:
callose, co-release, heavy metals, nutrient cations, Populus tremula, toxicity.
