CELLULAR MECHANISMS OF ALUMINUM TOXICITY AND RESISTANCE IN PLANTS

Aluminum (Al) toxicity is the major factor limiting crop productivity on acid soils, which comprise up to 40% of the world's arable lands. Also, many native and crop plants exhibit genetic-based variability in Al sensitivity that has allowed plant breeders to develop Al-resistant crops. Considerable research has been directed to elucidating the mechanisms of Al toxicity and resistance in recent years. However, these processes are still poorly understood. This review examines our current understanding of cellular mechanisms of Al toxicity and resistance. The major symptom of Al toxicity is a rapid inhibition of root growth, which has been proposed to be caused by a number of different mechanisms, including Al interactions within the cell wall, the plasma membrane, or the root symplasm. Al resistance has been speculated to be the result of either exclusion of Al from the root apex or the tolerance of symplasmic Al. This review focuses on those mechanisms for which some evidence exists as well as on some controversial aspects of Al phytotoxicity and resistance.