CHEMOPERCEPTION OF MICROBIAL SIGNALS IN PLANT-CELLS

Plants have exquisitely sensitive chemoperception systems for signal substances derived from microorganisms. Among the microbial substances that plants can perceive at threshold concentrations of approximately 10(-12)-10(-10) M are oligosaccharides and lipo-oligosaccharides, peptides and glycopeptides, and lipophilic substances such as ergosterol. In many cases, the perception systems of plants recognize ''non-self' molecules characteristic of fungi and bacteria with a high degree of specificity, and some of them show rapid desensitization, leading to a refractory state reminiscent of smell perception. Specific binding sites for microbial signal molecules have been found on intact plant cells and on isolated plasma membranes; they probably function as receptor;. An intriguing question is whether the products of some of the recently identified resistance genes are homologous to such receptors. Chemoperception of microbial substances may not only play a role for the plant in active defense and pathogen resistance, but also in mutualistic symbiosis and in the acquisition of basic information about microbes in the environment.