Phytohormones and other plant growth regulators produced by PGPR: The genus Azospirillum

Abstract

One of the fi rst mechanisms proposed to explain the plant growth promotion due to bacterial inoculation has been the nitrogen biological fi xation; however, this mechanism has been of less agronomic signifi cance than was initially expected. In counterpart, other mechanisms have been proposed to explain these inoculation effects, such as production of phytohormones and other plant growth regulators. Nowadays, we know that benefi c effect of inoculation with rhizobacteria can be correlatedwith production and metabolism of chemically defi ned compounds such asauxins, cytokinins, gibberellins, and other plant growth regulators, such as abscisic acid and nitric oxide. In this chapter, we highlight the analytical and biological methods used to identify and quantify the most relevant phytohormones and plant growth regulators produced by Azospirillum sp. and other benefi c rhizobacteria.