This thesis is an investigation of two possible mechanisms of disease resistance against 'Pseudomonas aeruginosa' O6ad in ' Nicotiana tahacum' expressing an immunoglobulin G against lipopolysaccharide (LPS) of 'P. aeruginosa' O6ad. The mechanisms examined were that the antibody directly affects 'P. aeruginosa' O6ad cells, and that the antibody affects LPS signalling. Purified antibody specifically inhibits growth and survival of the pathogen on binding to LPS of ' P. aeruginosa' O6ad (LPS'P.a.'O6ad ) 'in vitro'. However, in the transgenics inoculated with 'P. aeruginosa' O6ad cells, there is a reduction in ' P. aeruginosa' O6ad populations, although the antibody in the endoplasmic reticulum appears to be spatially separated from 'P. aeruginosa' O6ad in the apoplast. Furthermore, pretreatment of the transgenics with LPS' P.a.'O6ad results in a zone of LPS'P.a. 'O6ad along the plant cell walls, internalization of LPS'P.a.'O6ad in the cytoplasm, and reduction of 'P. aeruginosa' O6ad populations, suggesting that the antibody is affecting LPS'P.a.' O6ad signalling in planta.