Evaluation of indole-3-acetic acid homeostasis in Bradyrhizobium japonicum E109.

PIERANTONELLI, MARÍA BELÉN; MOLINA, ROMINA; TORRES, DANIELA; SPAEPEN, S.; VANDERLEYDEN., J; CASSAN, FABRICIO

Shangai

Congreso; 21 Conferencia de la Asociación Internacional de Sustancias Reguladores del Crecimiento de Plantas (IPGSA).; 2013

International Plant Growth Regulation Substances Assosiation

Indole-3-acetic acid (IAA) is one of the most important molecules produced by Brayrhizobium japonicum during legume-rhizobia symbiosis. Several conjugates of IAA with amino acids (IAA-amides), as well as the IAA-amides hydrolysis had been described in both, bacteria and plants. Our hypothesis states that IAA-amides could be hydrolyzed and metabolized by B. japonicum in culture medium. B. japonicum E109, the strain mostly used for soybean seeds inoculation in Argentina, was pre-incubated at 30°C and 200 rpm in orbital shacking in 250 ml flask containing 100 ml YEM medium plus 10 mg.l-1 L-tryptophan until exponential growth phase (OD595: 0.1), then fractionated in 5 ml aliquots and individually supplemented with 5 µl of 10 mg.ml-1 IAA-alanine, IAA-phenylalanine or IAA-leucine solutions. Control treatments were performed by addition of IAA, indole-3-butyric acid (IBA), naphthalene acetic acid (NAA), gibberellic acid (GA3) or Zeatin (Z). Another group of treatments were performed by addition of 10 mM IAA plus 10 mg.ml-1 L-alanine, L-phenylalanine, L-leucine solutions to evaluate the potential conjugation process in Bj. After 2, 4, 8, 12, 24, 48 hours of incubation, the following parameters were evaluated: cell biomass (OD595); cellular viability (CFU.ml-1); IAA and related molecules (μg.ml-1) by HPLC. The IAA homeostasis in B. japonicum E109 was evaluated. No evidence for IAA conjugation was observed; however a strong catabolic activity was established in all treatments with exogenous addition of IAA, IBA or NAA. About the hydrolysis of IAA-amides, B. japonicum shown capacity to produce free IAA and quickly catabolize this molecule. These results allow us to speculate about non reported mechanism of IAA homeostasis in B. japonicum.