Malate-permeable channels and cation channels activated by aluminum in the apical cells of wheat roots.
Aluminum (Al(3+))-dependent efflux of malate from root apices is a mechanism for Al(3+) tolerance in wheat (Triticum aestivum). The malate anions protect the sensitive root tips by chelating the toxic Al(3+) cations in the rhizosphere to form non-toxic complexes. Activation of malate-permeable channels in the plasma membrane could be critical in regulating this malate efflux. We examined this by investigating Al(3+)-activated channels in protoplasts from root apices of near-isogenic wheat differing in Al(3+) tolerance at a single locus. Using whole-cell patch clamp we found that Al(3+) stimulated an electrical current carried by anion efflux across the plasma membrane in the Al(3+)-tolerant (ET8) and Al(3+)-sensitive (ES8) genotypes. This current occurred more frequently, had a greater current density, and remained active for longer in ET8 protoplasts than for ES8 protoplasts. The Al(3+)-activated current exhibited higher permeability to malate(2-) than to Cl(-) (P(mal)/P(Cl) > or = 2.6) and was inhibited by anion channel antagonists, niflumate and diphenylamine-2-carboxylic acid. In ET8, but not ES8, protoplasts an outward-rectifying K(+) current was activated in the presence of Al(3+) when cAMP was included in the pipette solution. These findings provide evidence that the difference in Al(3+)-induced malate efflux between Al(3+)-tolerant and Al(3+)-sensitive genotypes lies in the differing capacity for Al(3+) to activate malate permeable channels and cation channels for sustained malate release.
School of Biological Sciences, The Flinders University of South Australia, G.P.O. Box 2100, Adelaide, South Australia 5001, Australia. wenhao.zhang@flinders.edu.au
W H
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Zhang
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Ryan
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Tyerman
D000535:Aluminum / Q000494:pharmacology*; D001692:Biological Transport; D000242:Cyclic AMP / Q000494:pharmacology; D007473:Ion Channels / Q000378:metabolism*; D008293:Malates / Q000378:metabolism*; D009544:Niflumic Acid / Q000494:pharmacology; D010539:Permeability; D018517:Plant Roots / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D014908:Triticum / Q000378:metabolism*; D062367:ortho-Aminobenzoates / Q000494:pharmacology
D007473:Ion Channels; D008293:Malates; D062367:ortho-Aminobenzoates; D009544:Niflumic Acid; C001209:fenamic acid; D000535:Aluminum; D000242:Cyclic AMP