Root colonization and nodC gene induction in the peanut- rhizobia interaction under acidic conditions

ANGELINI, J.; CASTRO, S.; FABRA, A.

BIOCELL

Lugar: Mendoza (Argentina); Año: 2002 vol. 26 p. 89 - 89

0327-9545

Legumes are very important not only agriculturally but also ecologically because they are responsible for the majority of the global flux of nitrogen from atmospheric nitrogen to ammonia. initial root colonization by rhizobia is one of the early steps of the symbiotic process preceding root invasion. To visualise peanut root colonization strains of native bacteria containing the plasmid pTB93F were used. using the spot inoculation method. nodC gene induction was measured as b-galactosidase activity and reported as Miller units. Here we demonstrated that, in the peanut-rhizobia interaction, this process was affected when both acid tolerant or acid sensitive bacteria were grown at low pH (5.5). This elect effect seem to be a result of alterations produced by the acidity on the microsynibiont and not on its host. We determined that. at pH7, al1 the flavonoids assayed were able to induce the nodC gene expression but at different levels. At acid pH, very low induction was observed in acid sensitive isolates. Exudates released by peanut roots growing in an acid medium seem not to be altered in their ability to induce nodC gene activity. Thus, our results provide evidence that peanut rhizobia are more sensitive at acid pH than their legume host.