Attachment ofBradyrhizobium japonicumto the roots and curling of the root hairs of various legumes and non-legumes

Abstract

Abstract Rhizobia, members of the genera Rhizobium, Bradyrhizobium, and Azorhizobium, have the ability to elicit the formation of nitrogen-fixing nodules on the roots of their leguminous host plants. The symbiotic association between rhizobia and leguminous plants is highly specific: a particular bacterial species can nodulate only a limited number of plant species. The host-specific aspect of this symbiosis has led to the identification of cross-inoculation groups in which each bacterial species is classified according to its group of host plants. Nodule-like structures, invaded by rhizobia, have been induced on the roots of non-leguminous plants, namely, wheat, rice, oilseed rape, and barley, by the addition of the synthetic auxin 2,4-dichlorophenoxyacetic acid (Tchan and Kennedy 1989; Ridge et al. 1992), by treatment with cell wall-degrading enzymes (Al-Mallah et al. 1989, 1990), or by the application of a magnetic field (ling et al. 1990). These findings prompted us to reexamine the nature of the factors controlling host-specific nodulation.