%D 2006 %0 ARTICLE %T Citrate transporters play a critical role in aluminium-stimulated citrate efflux in rice bean ( Vigna umbellata ) roots . %J Ann . Bot . %V 97 ( 4 ) %P 579-84 %A Yang JL %A Zhang L %A Li YY %A You JF %A Wu P %A Zheng SJ %M pub16446286 %X 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 microm 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 microm 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 microm ) 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 .