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Plants have evolved a number of different mechanisms for dealing with toxic metals in the environment, and these can involve both avoidance (exclusion of the metal from a plant tissue/organ) or true tolerance, which presumably involves chelation and/or sequestration of the metal in an internal compartment. The best characterized mechanism of plant metal tolerance is associated with crop aluminum (Al) tolerance. Al toxicity is a worldwide problem that arises when soil pH values drop to 5 or below; in these acidic soils rhizotoxic forms of Al are solubilized into the soil solution, damaging roots and resulting in reduced water and nutrient uptake. This talk will focus on a major Al tolerance mechanism which involves Al exclusion from the root tip mediated by Al activation of specialized transporters that release organic acids into the rhizosphere, where they chelate and prevent Al from entering the root. Several Al tolerance genes have been cloned recently and these belong to two different families of novel membrane transporters. The function and regulation of these tolerance genes will be discussed, as well as the implications of these findings in facilitating plant improvements for growth on degraded or marginal soils.

Plants have evolved a number of different mechanisms for dealing with toxic metals in the environment, and these can involve both avoidance (exclusion of the metal from a plant tissue/organ) or true tolerance, which presumably involves chelation and/or sequestration of the metal in an internal compartment. The best characterized mechanism of plant metal tolerance is associated with crop aluminum (Al) tolerance. Al toxicity is a worldwide problem that arises when soil pH values drop to 5 or below; in these acidic soils rhizotoxic forms of Al are solubilized into the soil solution, damaging roots and resulting in reduced water and nutrient uptake. This talk will focus on a major Al tolerance mechanism which involves Al exclusion from the root tip mediated by Al activation of specialized transporters that release organic acids into the rhizosphere, where they chelate and prevent Al from entering the root. Several Al tolerance genes have been cloned recently and these belong to two different families of novel membrane transporters. The function and regulation of these tolerance genes will be discussed, as well as the implications of these findings in facilitating plant improvements for growth on degraded or marginal soils.