Malate-permeable channels and cation channels activated by aluminum in the apical cells of wheat roots
Date
2001
Authors
Zhang, W.
Ryan, P.
Tyerman, S.
Editors
Advisors
Journal Title
Journal ISSN
Volume Title
Type:
Journal article
Citation
Plant Physiology, 2001; 125(3):1459-1472
Statement of Responsibility
Wen-Hao Zhang, Peter R. Ryan, and Stephen D. Tyerman
Conference Name
Abstract
Aluminum (Al³⁺)-dependent efflux of malate from root apices is a mechanism for Al³⁺ tolerance in wheat (Triticum aestivum). The malate anions protect the sensitive root tips by chelating the toxic Al³⁺ 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 Al³⁺-activated channels in protoplasts from root apices of near-isogenic wheat differing in Al³⁺ tolerance at a single locus. Using whole-cell patch clamp we found that Al³⁺ stimulated an electrical current carried by anion efflux across the plasma membrane in the Al³⁺-tolerant (ET8) and Al³⁺-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 Al³⁺-activated current exhibited higher permeability to malate²⁻ than to Cl⁻ (Pmal/PCl ≥ 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 Al³⁺ when cAMP was included in the pipette solution. These findings provide evidence that the difference in Al³⁺-induced malate efflux between Al³⁺-tolerant and Al³⁺-sensitive genotypes lies in the differing capacity for Al³⁺ to activate malate permeable channels and cation channels for sustained malate release.