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Plant Physiol, March 2001, Vol. 125, pp. 1473-1484
The High Level of Aluminum Resistance in Signalgrass Is Not
Associated with Known Mechanisms of External Aluminum Detoxification in
Root Apices1
Peter
Wenzl,2*
Gloria M.
Patiño,
Alba L.
Chaves,
Jorge E.
Mayer, and
Idupulapati M.
Rao
Centro Internacional de Agricultura Tropical, A.A. 6713, Cali,
Colombia (P.W., G.M.P., A.L.C., I.M.R.); Institut für
Pflanzenphysiologie, Universität Wien, A-1090 Vienna, Austria
(P.W.); and Center for the Application of Molecular Biology to
International Agriculture, G.P.O. Box 3200, Canberra ACT 2601, Australia (J.E.M.)
Al resistance of signalgrass (Brachiaria
decumbens Stapf cv Basilisk), a widely sown tropical forage
grass, is outstanding compared with the closely related ruzigrass
(Brachiaria ruziziensis Germain and Evrard cv Common)
and Al-resistant genotypes of graminaceous crops such as wheat,
triticale, and maize. Secretion of organic acids and phosphate by root
apices and alkalinization of the apical rhizosphere are commonly
believed to be important mechanisms of Al resistance. However, root
apices of signalgrass secreted only moderately larger quantities of
organic acids than did those of ruzigrass, and efflux from signalgrass
apices was three to 30 times smaller than from apices of Al-resistant
genotypes of buckwheat, maize, and wheat (all much more sensitive to Al
than signalgrass). In the presence, but not absence, of Al, root apices
of signalgrass alkalinized the rhizosphere more than did those of
ruzigrass. The latter was associated with a shortening of the
alkalinizing zone in Al-intoxicated apices of ruzigrass, indicating
that differences in alkalinizing power were a consequence, not a cause
of, differential Al resistance. These data indicate that the main
mechanism of Al resistance in signalgrass does not involve external
detoxification of Al. Therefore, highly effective resistance mechanisms
based on different physiological strategies appear to operate in this species.
1
This work was supported by the Kommission
für Entwicklungsfragen of the Austrian Academy of Sciences, and
by the Colombian Ministry of Agriculture and Rural Development.
2
Present address: Center for the Application of Molecular
Biology to International Agriculture, G.P.O. Box 3200, Canberra ACT 2601, Australia.
*
Corresponding author; e-mail peter{at}cambia.org.au; fax
61-2-6246-4501.
© 2001 American Society of Plant Physiologists
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