The Mechanisms for Self-Protection Against Bacterial Phytotoxins*

Abstract

Evidence has been accumulating that selected phytopathogenic bacteria pro­ duce phytotoxins important for disease development. These toxins elicit the development of most of the commonly observed symptoms of diseases caused by these pathogens, including chlorosis, growth abnormalities, necrosis, watersoaking, and wilting. They are considered to be virulence factors (52) and are non-host-selective-although this is not a required property but simply reflects the fact that compelling evidence to the contrary has not yet been presented. Although the details of their mechanisms of action are still incompletely understood, we do have knowledge in a few well-studied cases about their sites of action and some information on the physico-chemical events linking these primary interactions to symptom expression (7, 32, 36). Such studies have shown that many, but certainly not all, of these toxins' sites of action, or targets, occur not only in the host but also in the bacterium that produces the toxin. This raises the question of how these pathogens have avoided suicide (5). What kinds of mechanisms for self-protection do they possess?