Mechanisms of adaptation to high aluminum condition in native plant species growing in acid soils: A review

Watanabe T, Osaki M

COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS 33 (7-8): 1247-1260 2002

Abstract: Various studies of the mechanisms of aluminum (Al) tolerance in crop plants have been conducted to improve crop productivity in acid soils. However, many native plant species vigorously grow in acid soils. These species have adapted well to high levels of Al in the medium. The mechanisms of this adaptation can be separated into Al exclusion and internal Al inactivation. In general. plant species that have developed mechanisms of the former type are called "Al excluders," and those that have developed mechanisms of the latter type are called "Al accumulators." Mechanisms of Al exclusion in excluder species have not been completely elucidated, and may involve some strong mechanisms in addition to the exudation of organic acid from roots. Al accumulator species are supposed to create an Al-ligand (mainly organic acids) complex for translocation from roots to shoots, and for accumulation in the leaves. Interestingly, the ligand of Al for translocation often differs from that for storage in the leaves. In addition, Al accumulator species seem to prevent the toxic effect of Al on the metabolism in leaves by means of isolating the Al in sites that are insensitive to Al (e.g., epidermal cells or vacuoles). Growth in some native plant species that have adapted to acid soils is enhanced by Al application. This Al-induced growth enhancement is considered to be caused by Al-induced stimulation of nutrient uptake in Al excluders (nonaccumulators), and by physiological effects of Al itself in addition to the stimulation of nutrient uptake in accumulators. Elucidation of these mechanisms of adaptation to high levels of Al in medium will be useful for improved production of Al-tolerant crop cultivars and rehabilitation of forest areas.