The Role of Salicylates in RHIZOBIUM-Legume Symbiosis and Abiotic Stresses in Higher Plants

Abstract

Salicylic acid (SA) is an endogenous plant growth regulator. SA is involved in various physiological processes of plant growth and development and plays an active role in plant defense responses. SA also plays a major role during the early stages of Rhizobium-legume symbiosis. Nod factors produced by rhizobia, in response to legume produced flavonoids, affect SA content of the host plant during the early stages of nodulation. On the other hand, SA inhibits bacterial growth and the production of Nod factors by rhizobia. Exogenous application of SA delays nodule formation and decreases the number of nodules at the roots of the host plant. SA protects plants under abiotic stresses such as drought, salinity, low and high temperatures, and the damaging action of heavy metals. The ability of SA to protect plants exposed to abiotic stresses is due to the induction of a series of signal transduction cascades leading to the expression of genes responsible for the protection of plants from the stress.