Vdm

ES/Oh ET/Oh ES/8h ET/8h ES/24hET/24h Wheat variety/treatment

| Fig. 1.8.2. Extrusion of ions from the root tips of Al3+-sensitive and -tolerant wheat varieties by incubation of seedlings in 100 nM Al solution for 0, 8 and 24 h. A Mg , Al and CI content of dried root tips, gous, sensitive line, ET homozygous, tolerant line. (After Delhaize et al. 1993a)

P, S and K content. ES Homozy-

that the latter penetrates through Mg2+ channels, which can be seen by the concomitant reduction of Mg2+ uptake or by a decreased Mg2+ content (Fig. 1.8.2). Because of the similar ionic radius, the Al3+ ion might also use the siderophore uptake system for Fe3+, which is well developed in grass roots.

Finally, it cannot be excluded that positively charged A1 ions adsorb at the external side of the plasma membrane and reach the cytosol via endocytosis. Al3+ does not interact with K+ channels and, considering the usually high K+/ Al3+ ratio, has therefore almost no influence on the membrane potential.

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