Bacterial pathogens must enter the plant tissue in order to cause a successful infection. Foliar bacterial pathogens that are not able to directly penetrate the plant epidermis rely on wounds or natural openings to internalize leaves. This protocol describes a procedure to estimate the population size of Pseudomonas syringae in the leaf apoplast after surface inoculation of Arabidopsis rosettes.

Coronatine is a polyketide phytotoxin produced by several pathovars of the plant pathogenic bacterium Pseudomonas syringae. It is one of the most important virulence factors determining the success of bacterial pathogenesis in the plant at both epiphytic and endophytic stages of the disease cycle. This protocol describes an optimized procedure to culture bacterial cells for coronatine production and to quantify the amount of coronatine secreted in the culture medium using an HPLC-based method.