ACC9, P. tolaasii ACC23 and Mycobacterium sp. ACC14 stimulated root elongation to the same extent regardless of whether the plants had been treated with Cd2+; in contrast, Alcaligenes sp. ZN4 stimulated root elongation more markedly in untreated plants. No correlation was found between ACCD activity in vitro and PREP activity in untreated seedlings, but the correlation with PREP activity seems to become significant in Cd-treated seedlings. Taxonomic position and species-specific interactions between bacteria and root associated with other PGP traits could affect the relationship between rhizobacteria and plants roots. Three of the bacterial strains tested produced IAA, and two of them produced siderophores.