Pseudomonas cichorii SPC9001 was transformed with plasmid pNP126 containing luxCDABE operon of Vibrio fisheri, and bioluminescent IBRC82 was obtained. Growth and movement of IBRC82 and the response of host tissue were successively observed in the same lettuce leaf using the video-intensified microscopy (VIM) camera equipped with the ARGUS 50. Bacterial bioluminescence conferred by the lux operon was first observed at inoculated sites 2 days after inoculation and then in the surrounding region. It then moved along the leaf veins. Browning symptoms appeared in areas where bioluminescence had been detected and developed into bacterial rot. Microscopic observation showed that P. cichorii colonized the intercellular spaces of the epidermis and mesophyll and then moved into the vascular bundle. These results suggest that the disease symptom appears and develops, following the bacterial growth and movement in a lettuce leaf. In leaf disks infiltrated with the bioluminescent bacteria, bioluminescence was observed in the whole tissue 12hr after inoculation, and the disks then collapsed 36hr after inoculation. Cycloheximide, a eukaryote-specific protein synthesis inhibitor, completely suppressed the collapse of infiltrated disks, but had no effect on bacterial bioluminescence. These results demonstrate that the collapse of infiltrated disks following bacterial bioluminescence requires protein synthesis in the lettuce leaf. Therefore, the disease symptom appears and develops depending on the response of host tissues, including de novo protein synthesis, corresponding to the bacterial growth and movement in a lettuce leaf.