Basic and Technological Aspects of Phytohormone Production by Microorganisms: Azospirillum sp. as a Model of Plant Growth Promoting Rhizobacteria

Abstract

The functional analysis of phytohormones production, interaction, and regulation in higher plant has re-emerged in the last 10 years due to incredible advances in integrative study models; however, plants are not alone in natural conditions and usually are colonized or influenced directly by different types of microorganisms such as rhizobacteria many of which have the ability to produce phytohormones. This chapter concentrates information related to the biosynthesis, metabolism, regulation, physiological role, and agronomical impact of phytohormones produced by microorganisms with an emphasis on the plant growth promoting rhizobacteria belonging to the Azospirillum genus, considered to be one of the most representative and worldwide studied bacterial genera during the last 30 years. This review contains exhaustive information about the phytohormones auxins, gibberellins, cytokinins, ethylene, abscisic acid and jasmonates, as well as the plant growth regulators polyamines and nitric oxide; biosynthesized or metabolized by Azospirillum sp. and other growth promoting rhizobacteria in chemically defined medium or plant interaction conditions.