Aluminum Toxicity

High aluminum (Al) concentrations in acid soils represent one of the biggest constraints to world agricultural production. This is caused by Al inhibiting root growth, and consequently water and nutrient uptake, which then leads to poor crop development and low yields. Aluminum prevents root development by interfering with cell wall and plasma membrane expansion as well as by disrupting nutrient uptake and cell signaling processes. Some plants can overcome this toxicity by releasing organic acid anions (e.g., citrate and malate) into the soil which form complexes with Al³⁺ and render it nontoxic. The genes encoding this resistance mechanism are now known and their transfer to other crop plants has been shown to confer tolerance. This has provided a low-cost technological solution allowing greater crop production on acid soils. Other plants, naturally adapted to grow on acid soils, are known to hyperaccumulate Al in their tissues, although the reasons for this are still poorly understood.