AOBPreview originally published online on January 30, 2006
Annals of Botany 2006 97(4):579-584; doi:10.1093/aob/mcl005
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Citrate Transporters Play a Critical Role in Aluminium-stimulated Citrate Efflux in Rice Bean (Vigna umbellata) Roots
1 College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310029, China and 2 Key State Laboratory of Plant Physiology and Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou 310029, China
* For correspondence. E-mail sjzheng{at}zju.edu.cn
Received: 4 October 2005 Returned for revision: 29 November 2005 Accepted: 5 December 2005 Published electronically: 30 January 2006
• Background and Aims Aluminium (Al) stimulates the efflux of citrate from apices of rice bean (Vigna umbellata) roots. This response is delayed at least 3 h when roots are exposed to 50 µM Al, indicating that some inducible processes leading to citrate efflux are involved. The physiological bases responsible for the delayed response were examined here.
• Methods The effects of several antagonists of anion channels and citrate carriers, and of the protein synthesis inhibitor, cycloheximide (CHM) on Al-stimulated citrate efflux and/or citrate content were examined by high-pressure liquid chromatography (HPLC) or an enzymatic method.
• Key Results Both anion channel inhibitors and citrate carrier inhibitors can inhibit Al-stimulated citrate efflux, with anthracene-9-carboxylic acid (A-9-C, an anion channel inhibitor) and phenylisothiocyanate (PI, a citrate carrier inhibitor) the most effective inhibitors. A 6 h pulse of 50 µM Al induced a significant increase of citrate content in root apices and release of citrate. However, the increase in citrate content preceded the efflux. Furthermore, the release of citrate stimulated by the pulse treatment was inhibited by both A-9-C and PI, indicating the importance of the citrate carrier on the mitochondrial membrane and the anion channel on the plasma membrane for the Al-stimulated citrate efflux. CHM (20 µM) also significantly inhibited Al-stimulated citrate efflux, confirming that de novo protein synthesis is required for Al-stimulated citrate efflux.
• Conclusions These results indicate that the activation of genes possibly encoding citrate transporters plays a critical role in Al-stimulated citrate efflux.
Key words: Aluminium resistance, anion channel, citrate carrier, inhibitor, organic acid anions, protein synthesis, rice bean, toxicity, transporter, Vigna umbellata
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