ABSTRACT
This chapter reviews the known aspects of microbial biosynthesis of phytohormones and their effects on plants' growth and development. Phytohormones coordinate information coming from many sources and circulating within plants through many points of regulation, from biosynthesis to transduction. Microbial production of ethylene, for example, can be accomplished from a number of structurally unrelated compounds. Phytohormones perform many functions in plants, and it is common for a function attributed to one group of hormones to overlap with the functions of other groups. Phytohormones produced by rhizosphere microorganisms or provided by inoculation in the root vicinity certainly affect the growth and development of plants after being taken up by the roots. Phytohormone production is one of the major mechanisms by which microbes can induce beneficial effects, not only by stimulating plant growth but also by inducing abiotic and biotic stress tolerance in crop plants.
