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Previous studies in our laboratory demonstrated that the attachment of Azospirillum brasilense Cd to maize and wheat roots was altered when the bacteria were grown under saline stress. The aim of this work was to analyze the interaction when either the plant or both components were exposed to saline conditions. We demonstrated that this stress altered the early stages of development, in this plant model, leading to an inadequate colonization. The effect of saline stress on the expression of A. brasilense N2 fixation gene promoters was also studied. While nifA expression was increased in stressed bacteria, nifH transcription was diminished, suggesting an alteration in the NifA activation process. The induction of the nif gene transcription by root exudates was investigated, and the results suggest that they could be modulating certain bacterial processes, such as nitrogen fixation. However, stressed bacteria did not respond to the exudate's action. This could be related to the modified membrane composition resulting from changes in proteins, glucans, and capsular, exo- and lipopolysaccharides. We conclude that saline stress alters the Azospirillum brasilense Cd - maize interaction, the normal colonization, and the nitrogen fixation process.Key words: Azospirillum brasilense, saline stress, Azospirillum-root interaction, exudates, nif genes.

The present work was designed to study the effect of saline stress on the attachment of Azospirillum brasilense to maize and wheat roots. We demonstrate that both attachment steps (adsorption and anchoring) are altered. A 100-kDa protein disappeared under these experimental conditions. Coincidently, a 100-kDa flagellum protein has been identified as the agent responsible for adsorption. However, the adhesive properties of bacteria appear to involve other factors, such as the ionic strength of the medium. The impairment of anchoring ability was correlated with alterations in exopolysaccharide, glucan, and lipopolysaccharide contents.Key words: Azospirillum brasilense, saline stress, Azospirillum-root interaction.

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