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 infection1–3. 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 detergents1–3. 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.