POSSIBLE INVOLVEMENT OF AL-INDUCED ELECTRICAL SIGNALS IN AL TOLERANCEIN WHEAT

The relationship between Al-induced depolarization of root-cell transm embrane electrical potentials (E-m) and Al tolerance in wheat (Triticu m aestivum L.) was investigated. Al exposure induced depolarizations o f E-m in the Al-tolerant wheat cultivars Atlas and ET3, but not in the Al-sensitive wheat cultivars Scout and ES3. The depolarizations of E- m occurred in root cap cells and as far back as 10 mm from the root ti p. The depolarization was specific to Al3+; no depolarization was obse rved when roots were exposed to the rhizotoxic trivalent cation La3+. The Al-induced depolarization occurred in the presence of anion-channe l antagonists that blocked the release of malate, indicating that the depolarization is not due to the electrogenic efflux of malate(2-). K-induced depolarizations in the root cap were of the same magnitude as Al-induced depolarizations, but did not trigger malate release, indic ating that Al-induced depolarization of root cap cell membrane potenti als is probably linked to, but is not sufficient to trigger, malate re lease.