Aluminum-Induced Inhibition of Root Growth: Roles of Cell Wall Assembly, Structure, and Function

Aluminum (Al) toxicity is the most important soil constraint for plant growth and development in acid soils. It is a matter of debate whether the primary lesions of Al toxicity are apoplastic or symplastic, while there is increasing physiological, biochemical, and molecular evidence showing that the modification of cell wall properties contributes to the Al-induced inhibition of root growth. The rapid binding of Al in the root cell wall particularly to the pectin matrix and hemicellulose can affect cell wall properties. Most recent studies have revealed that the local accumulation of auxin in the most Al-sensitive root zone of the root apex is a major factor leading to Al-induced root-growth inhibition. Evidence suggests that the auxin effect is mediated mainly via modification of cell wall structural properties. A further in-depth characterization of the Al-induced apoplastic reactions in the most Al-sensitive zone of the root apex is urgently required to better understand the phytohormone-mediated signaling network leading to Al-induced inhibition of root growth.