ALTERATIONS IN MEMBRANE-POTENTIAL AND IN PROTON EFFLUX IN PLANT-ROOTS INDUCED BY AZOSPIRILLUM-BRASILENSE

Inoculation of soybean seedlings with Azospirillum brasilense Cd significantly reduced the membrane potential in every root part and was being maximal in the root elongation zone. Monitoring the proton efflux pattern of inoculated wheat roots by several A. brasilense strains and by Pseudomonas sp. for prolonged periods (up to 200 h) revealed a change from the bimodal pattern of proton efflux of non inoculated roots. This change was not related to root colonization ability but to bacterial capacity to induce changes in root surface area. Continuous perfusion of the plant nutrient solution with a fresh solution (from inoculation time), eliminated the enhancing effect of inoculation on proton efflux. We propose that A. brasilense inoculation influences membrane activity and subsequently proton efflux in roots, probably through the release of an as yet unidentified bacterial signal.