Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/15/1998
Publication Date: N/A
Citation: Interpretive Summary: Large areas of land within the U.S. and a significant proportion of the world's arable lands are acidic. In these acid soils, the phytotoxic aluminum ion, Al3+, is solubilized from aluminosilicate clays and is quite toxic to root growth and function. Thus, aluminum (Al) toxicity is the primary factor limiting crop production on these acid soils. Understanding the physiological basis for Al toxicity and the cellular mechanisms that some plant species use to tolerate Al are essential in order to develop crop species that can be cultivated on these acid soils. In this paper, we studied a recently identified mechanism of Al tolerance in wheat that involves exclusion of the toxic Al ion from the root tip. This is facilitated by Al exposure triggering the release of specific organic acids from the root tip; these organic acids bind Al in the soil and keep it out of the root. Here we studied the nature of the signal that must result from Al exposure to roots that tells the root to release the organic acid. Studies into the electrical properties of root cells with microelectrodes indicated that this signal possibly is an Al-induced change in the voltage maintained across the root cell outer membrane, which could open channels in the membrane that allow the organic acid to flow out of the cell. These findings provide important information that should help us better understand how some crops tolerate Al in acid soils.
Technical Abstract: The relationship between Al-induced depolarization of root-cell transmembrane electrical potentials (Em) and Al-tolerance in wheat (Triticum aestivum L.) was investigated. Al exposure induced depolarizations of Em in the Al-tolerant wheat lines Atlas and ET3, but not in the Al-sensitive wheat lines Scout and ES3. The depolarizations of Em occurred in root cap cells and as far back as 10 mm from the root tip. The depolarization was specific to Al3+; no depolarization was observed when roots were exposed to the rhizotoxic trivalent cation, La3+. The Al-induced depolarization occurred in the presence of anion channel antagonists that blocked the release of malate, indicating that the depolarization is not due to the electrogenic efflux of malate2-. Potassium-induced depolarizations in the root cap were of the same magnitude as Al-induced depolarizations but did not trigger malate release, indicating that Al-induced depolarization of root cap cell membrane potentials is probably linked to but is not sufficient to trigger malate release.