Ultrastructure of Bacterial Penetration in Plants

Successful infection of a host plant by a pathogen involves the movement of the pathogen toward the host, attachment of the pathogen to the plant surface, penetration of the host by the pathogen, and the proliferation of the pathogen inside the host immediately following entrance. Thus, the motility of plant­ pathogenic bacteria (63), as well as the aerotaxis and chemotaxis of bacteria toward plant exudates and leachates (10,21,65), helps bacteria land on host plants. Electric charges (45) and surface structures of the plant and bacteria (29, 42, 74) determine the recognition and adsorption between host and bacteria. Bacterial proliferation following entrance aids establishment of bacteria in infection courts. For a general account of these phases of the infection process, the reader is referred to reviews by Goodman (27, 28) and Billing (7). This review focuses primarily on spatial relationships and ul­ trastructural interactions between bacteria and host tissues at sites of infection with special emphasis on scanning electron microscopy (SEM) and transmis­ sion electron microscopy (TEM) of the movement of bacteria from the outside to the inside of a plant tissue.