PURIFICATION AND STRUCTURAL DETERMINATION OF A PHYTOTOXIC SUBSTANCE FROM EXSEROHILUM-TURCICUM

A peptide secreted by the fungus Exserohilum turicicum, the causal age nt of northern leaf blight of corn, was purified. The chemical structu re of the peptide was analyzed and two chemical structures are propose d. The peptide is composed of three amino acids in the following seque nce: glycine-serine-glutamine. The two proposed chemical structures di ffer by the degree of hydration of the molecule. One of the proposed p eptides was synthesized. Both the synthetic and the natural peptide in hibited chlorophyll synthesis of etiolated corn leaves. The peptide ex hibited genotypic specific activity at concentrations of 75 and 100 mg ml(-1). Ar higher concentrations the generic specific activity was no t observed. The synthesized compound inhibited root elongation of corn seedlings. The peptide was detected in infected corn leaves 2 days af ter inoculation and reached maximal levels 4 days after inoculation. T he peptide was also detected in a conidial water suspension during con idial germination. The importance of this compound in Northern leaf bl ight pathogenesis is discussed. (C) 1995 Academic Press Limited