Recent progress in the research of external Al detoxification in higher plants: a minireview.

Aluminum (Al) is highly toxic to plant growth. The toxicity is characterized by rapid inhibition of root elongation. However, some plant species and cultivars have evolved some mechanisms for detoxifying Al both internally and externally. In this review, the recent progress made in the research of external detoxification of Al is described. Accumulating evidence has shown that organic acids play an important role in the detoxification of Al. Some plant species and cultivars respond to Al by secreting citrate, malate or oxalate from the roots. Recently, the anion channel of malate and citrate in the plasma membrane has been characterized and a gene encoding the malate channel has been cloned. The metabolism of organic acids seems to be poorly correlated with the Al-induced secretion of organic acid anions. A number of QTLs (quantitative trait loci) for Al resistance have been identified in rice, Arabidopsis, and other species. Transgenic plants with enhanced resistance to Al have also been reported, but introduction of multiple genes may be required to gain high Al resistance in future.