エリシターによる高等植物の二次代謝活性の誘導

抄録

Plant cell cultures are potentially rich sources of useful phytochemicals but relatively few cultures can synthesize these metabolites. Expression of genetic informations on the secondary metabolism is thought to be generally repressed in such actively proliferating cells. It would be beneficial to be able to "switch on" the repressed activities by the addition of a specific inducer to these cultures but the control mechanism is, at present, only poorly understood. Microbial infection often induces the production of antibiotic substances in plant cells and the molecules which stimulate their synthesis have been called elicitors. The elicitors include various carbohydrates and glycoproteins derived from the cell walls of fungi and plants. These molecules may bind to certain receptor site on the surface of plant cells. We obtained evidence showing that these receptors transduce the external stimuli into an intracellular signal system partly via activation of phosphoinositol cycle as in animal cells, and partly via activation of adenylate cyclase which converts ATP into cAMP. In the latter case, cAMP stimulates Ca²⁺ influx from external space without participating cAMP-dependent protein kinase. These processes activate various Ca²⁺ (and calmodulin)-dependent protein kinases by increasing the level of free Ca²⁺ in the cytoplasm and somehow trigger the cellular responses which may include alterations in gene expression. Recent studies suggest that the increased synthesis of secondary metabolites in response to elicitation of various types appears to be not limited to the defense mechanism but the general response of cultured plant cells.