The Use of Monoclonal Antibodies to Investigate Plant-Microbe Interactions in Pea Root Nodules Containing Rhizobium Leguminosarum

The plant-microbe interactions that characterise the Rhizobium-legume symbiosis may be divided somewhat arbitrarily into those concerned with nutritional interactions (biotrophy) and those concerned with nodule development (morphogenesis). At the most intimate stage in the symbiosis, several thousand Rhizobium bacteroids are sustained within each infected plant cell. The host plant maintains a microaerobic oxygen concentration in the vicinity of the bacteroids, sufficient to permit oxidative respiration without denaturation of the highly oxygen-sensitive nitrogen fixation enzyme system. The host plant cells also regulate the supply of respiratory substrates needed by the bacteroids, and assimilate ammonia produced and excreted as a result of N2 fixation. However, before these elaborate physiological interactions can take place, another series of Rhizobium-legume interactions must occur in order to bring about the specific infection of legume roots by Rhizobium and the subseguent differentiation of the highly organised legume nodule structure. As our understanding of these morphogenetic processes unfolds, it will be interesting to compare and contrast these symbiotic interactions with those between a plant and a microbial pathogen. Furthermore, the study of the infection processes for both microbial symbionts and microbial pathogens should help to extend our knowledge and understanding of the normal processes that govern plant cell organisation and morphogenesis.