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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Adenine Nucleotide Pool Perturbation Is a Metabolic Trigger for AMP Deaminase Inhibitor-Based Herbicide Toxicity^1,[OA]

Department of Biochemistry, Medical College of Wisconsin, Milwaukee, Wisconsin 53226 (R.L.S.); Department of Horticultural Sciences, Program in Plant Molecular and Cellular Biology, University of Florida, Gainesville, Florida 32611 (A.-L.P., R.J.F.); and Bayer CropScience GmbH, Werk Hoechst, 65926 Frankfurt am Main, Germany (B.L., S.D.L.)

AMP deaminase (AMPD) is essential for plant life, but the underlying mechanisms responsible for lethality caused by genetic and herbicide-based limitations in catalytic activity are unknown. Deaminoformycin (DF) is a synthetic modified nucleoside that is taken up by plant cells and 5'-phosphorylated into a potent transition state-type inhibitor of AMPD. Systemic exposure of Arabidopsis (Arabidopsis thaliana) seedlings to DF results in dose-dependent (150–450 nM) and time-dependent decreases in plant growth that are accompanied by 2- to 5-fold increases in the intracellular concentrations of all adenine ribonucleotides. No measurable rescue is observed with either hypoxanthine or xanthine (250 µM), indicating that downstream effects of AMPD inhibition, such as limitations in adenine-to-guanine nucleotide conversion or ureide synthesis, do not play important roles in DF toxicity. However, adenine (250 µM) acts synergistically with a nontoxic dose of DF (150 nM) to produce growth inhibition and adenine nucleotide pool expansion comparable to that observed with a toxic concentration of the herbicide alone (300 nM). Conversely, adenine alone (60–250 µM) has no measurable effects on these parameters. These combined results support the hypothesis that AMPD is the primary intracellular target for this class of herbicides and strongly suggest that adenine nucleotide accumulation is a metabolic trigger for DF toxicity. AMP binds to 14-3-3 proteins and can interrupt client interactions that appear to drive their distributions. Trichome subcellular localization of the phi isoform is disrupted within 8 to 24 h after seedlings are semisubmersed in a solution of DF (100 nM), further suggesting that disrupted 14-3-3 protein function plays a role in the associated herbicidal activity.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Richard L. Sabina (sabinar{at}mcw.edu).

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www.plantphysiol.org/cgi/doi/10.1104/pp.107.096487

^* Corresponding author; e-mail sabinar{at}mcw.edu; fax 414–456–6510.

Received January 24, 2007; accepted February 6, 2007; published February 16, 2007.

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