Search

Aluminum (Al) toxicity is the main limiting factor of crop growth in acid soil. Plants can resist Al toxicity by regulating a series of mechanisms. Many physiological functions have been developed to improve the Al tolerance in plants which can be briefly outlined as two mechanisms. One such well-documented mechanism is external exclusion, which mainly reduces Al entry into cells, and the other one is the internal detoxification, consisting of the antioxidant defense system, the redistribution of Al3+ such as vacuolar compartmentalization, and the response of auxin. In external exclusion mechanism, with special emphasis on the mechanism of Al-induced organic acid secretion from roots, the current understanding of genes regulating organic acid secretion has been reviewed. In terms of the internal detoxification mechanism, we generalized the deposition and redistribution of Al in the cytoplasm, particularly, summarized the genes encoding Al3+ absorption and transport, and also discussed other possible mechanisms for improving plant tolerance to Al. Therefore, this review describes the recent research progress of Al tolerance mechanisms in plants, and provide future perspectives regarding more practical approaches for Al toxicity alleviation, which can create important social benefits and huge economic value for screening Al-tolerant plants and developing crop breeding. [ABSTRACT FROM AUTHOR]

Aluminum (Al) precipitates in acidic soils having a pH < 5.5, in the form of conjugated organic and inorganic ions. Al-containing minerals solubilized in the soil solution cause several negative impacts in plants when taken up along with other nutrients. Moreover, a micromolar concentration of Al present in the soil is enough to induce several irreversible toxicity symptoms such as the rapid and transient over-generation of reactive oxygen species (ROS) such as superoxide anion (O2•−), hydrogen peroxide (H2O2), and hydroxyl radical (•OH), resulting in oxidative bursts. In addition, significant reductions in water and nutrient uptake occur which imposes severe stress in the plants. However, some plants have developed Al-tolerance by stimulating the secretion of organic acids like citrate, malate, and oxalate, from plant roots. Genes responsible for encoding such organic acids, play a critical role in Al tolerance. Several transporters involved in Al resistance mechanisms are members of the Aluminum-activated Malate Transporter (ALMT), Multidrug and Toxic compound Extrusion (MATE), ATP-Binding Cassette (ABC), Natural resistance-associated macrophage protein (Nramp), and aquaporin gene families. Therefore, in the present review, the discussion of the global extension and probable cause of Al in the environment and mechanisms of Al toxicity in plants are followed by detailed emphasis on tolerance mechanisms. We have also identified and categorized the important transporters that secrete organic acids and outlined their role in Al stress tolerance mechanisms in crop plants. The information provided here will be helpful for efficient exploration of the available knowledge to develop Al tolerant crop varieties. [ABSTRACT FROM AUTHOR]