Diverse modes of action of biotic and abiotic phytoalexin elicitors

Abstract

PHYTOALEXINS are inducibly formed higher plant metabolites that are antibiotic to certain potential plant pathogens¹. At least 75 plant species representing 20 families have been shown to accumulate phytoalexins in response to infection^1–3. Phytoalexins also accumulate in plants in response to various agents termed elicitors¹, including substances of pathogen origin (biotic elicitors) and abiotic elicitors such as heavy metal salts and detergents^1–3. Elicitors may be useful for investigation of the molecular basis of phytoalexin production or disease resistance expression¹. However, the mechanisms by which such diverse elicitor molecules induce phytoalexin accumulation in plants are unknown. I have found⁴ that levels of glyceollin, a phytoalexin produced by soybean [Glycine max (L.) Merr.] hypocotyls in response to infection with the fungal pathogen Phytophthora megasperma var. sojae A. A. Hildb., are regulated by relative rates of induced biosynthesis and constitutive degrading activity. I report here the effects of various biotic and abiotic elicitors on biosynthesis and degradation of glyceollin in soybean tissues.