Planta

, Volume 196, Issue 1, pp 103–110

Characterisation of Al-stimulated efflux of malate from the apices of Al-tolerant wheat roots

  • Peter R. Ryan
  • Emmanuel Delhaize
  • Peter J. Randall
Article

DOI: 10.1007/BF00193223

Cite this article as:
Ryan, P.R., Delhaize, E. & Randall, P.J. Planta (1995) 196: 103. doi:10.1007/BF00193223

Abstract

Aluminium (Al) stimulates the efflux of malate from the apices of wheat (Triticum aestivum L.) roots (Delhaize et al. 1993, Plant Physiol. 103, 695–702). The response was five to tenfold higher in Al-tolerant seedlings than Al-sensitive seedlings and the capacity for Al-stimulated malate efflux was found to co-segregate with Al tolerance in a pair of near-isogenic wheat lines differing in Al-tolerance at a single dominant locus. We have investigated this response further using excised root apices. Half-maximal efflux of malate from apices of Al-tolerant seedlings was measured with 30 μM Al in 0.2 mM CaCl2, pH 4.2, while saturating rates of 2.0 nmol·apex−1·h−1 occurred with concentrations above 100 μM Al. The stimulation of malate efflux by Al was accompanied by an increase in K+ efflux which appeared to account for electroneutrality. The greater stimulation of malate efflux from Al-tolerant apices compared to Al-sensitive apices could not be explained by differences in the activities of phosphoenolpyruvate carboxylase or NAD-malate dehydrogenase. Several other polyvalent cations, including gallium, indium and the tridecamer Al13, failed to elicit malate efflux. Aluminium-stimulated efflux of malate was correlated with the measured concentration of total monomeric Al present, and with the predicted concentrations of Al3+ and AlOH2+ ions in the solution. Several antagonists of anion channels inhibited Al-stimulated efflux of malate with the following order of effectiveness: niflumic acid≈NPPB>IAA-94≈A-9-C>ethacrynic acid. Lanthanum, chlorate, perchlorate, zinc and α-cyano-4-hydroxycinnamic acid inhibited malate release by less than 30% at 100 μM while 4,4′-diisothiocyanatostilbene-2,2′-disulphonate (DIDS) had no effect. These results suggest that the Al3+ cation stimulates malate efflux via anion channels in apical cells of Al-tolerant wheat roots.

Key words

Aluminium (tolerance, toxicity) Anion channel Malate Root apex Triticum 

Abbreviations

A-9-C

anthracene-9-carboxylic acid

DIDS

4,4′-diisothiocyanatostilbene-2,2′-disulphonate

ET3, ET8, ES3, and ES8

Al-tolerant and Al-sensitive lines of wheat

IAA-94

[6, 7-dichloro-2-cyclopentyl-2, 3-dihydro-2-methyl-oxo-1H-inden-5-yloxy] acetic acid

NPPB

5-nitro-2-(3-phenylpropylamino)-benzoic acid

Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • Peter R. Ryan
    • 1
  • Emmanuel Delhaize
    • 1
  • Peter J. Randall
    • 1
  1. 1.CSIRO Division of Plant IndustryCanberraAustralia

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