Previous work led us to consider the role of nod gene-inducing compounds in related nodulating and non-nodulating Acacia species. Could the nodulation status of the non-nodulating plants be determined by an inability to produce and exude compounds that the related nodulating species were capable of delivering to the rhizobial symbionts? Also, it seemed to have been assumed previously that results gathered for extracts of seedlings or root tissue would reflect the situation for compounds exuded freely into the rhizosphere. The growth medium used in this investigation gave an opportunity to test this theory with the added bonus of allowing root exudates to be collected from a limited number of plants. The two non-nodulating species were found to lack neither the ability to produce potentially inducing compounds nor the means to exude them into the rhizosphere. However, it was demonstrated, through the distribution of potentially inducing compounds within the plants and their exudates, that the components of tissue extractions did not necessarily reflect the components exuded into the rhizosphere.
SHAW, J.E.M., REYNOLDS, T. AND SPRENT, J.I. (1997). A study of the symbiotic importance and location of nodgene inducing componds in two widely nodulating and two non-nodulating tropical tree species. Plant and Soil. 188. pp. 77-82. [DOI: 10.1023/A:1004212330945]