A STUDY OF THE SYMBIOTIC IMPORTANCE AND LOCATION OF NOD GENE INDUCINGCOMPOUNDS IN 2 WIDELY NODULATING AND 2 NONNODULATING TROPICAL TREE SPECIES

Previous work led us to consider the role of nod gene-inducing compoun ds in related nodulating and non-nodulating Acacia species. Could the nodulation status of the non-nodulating plants be determined by an ina bility to produce and exude compounds that the related nodulating spec ies were capable of delivering to the rhizobial symbionts? Also, it se emed to have been assumed previously that results gathered for extract s of seedlings or root tissue would reflect the situation for compound s exuded freely into the rhizosphere. The growth medium used in this i nvestigation gave an opportunity to test this theory with the added bo nus 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 ex ude them into the rhizosphere. However, it was demonstrated, through t he distribution of potentially inducing compounds within the plants an d their exudates, that the components of tissue extractions did not ne cessarily reflect the components exuded into the rhizosphere.