Many studies demonstrate the potential application of arbuscular mycorrhizal fungi (AMF) for remediation purposes, but little is known on AMF potential to enhance plant tolerance to arsenic (As) and the mechanisms involved in this process. We carried anatomical and ultrastructural studies to examine this symbiotic association and the characteristics of shoots and roots of Leucaena leucocephala in As-amended soils (35 and 75 mg As dm(-3)). The experiment used 3 AMF isolates from uncontaminated soils: Acaulospora morrowiae, Glomus clarum, and Gigaspora albida; a mixed inoculum derived from combining these 3 isolates (named Mix AMF); and, 3 AMF isolates from As-contaminated areas: A. morrowiae, G. Clarum and Paraglomus occultum. Phytotoxicity symptoms due to arsenic contamination appeared during plant growth, especially in treatments without AMF application. Inoculation with G. clarum and the mixture of species (A. morrowiae, G. albida, and G. clarum) resulted in better growth of L. leucocephala in soils with high As concentrations, as well as significant As removal from the soil, showing a potential for using AMF in phytoextraction. Light microscopy (LS), transmission (TEM) and scanning electron microscopies (SEM) studies showed the colonization of the AMF in plant tissues and damage in all treatments, with ultrastructural changes being observed in leaves and roots of L. leucocephala, especially with the addition of 75 mg dm(-3) of As. (C) 2012 Elsevier B.V. All rights reserved.