Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 7/27/1996
Publication Date: N/A
Technical Abstract: The cyclic tetrapeptide HC-toxin is a virulence determinant synthesized by Cochliobolus carbonum race 1 in culture and during infection of maize. To study specific nutritional factors affecting toxin production in culture, a defined medium lacking yeast extract was developed that supported growth and HC-toxin production. Extracts of media from cultures supplemented with various nitrogen sources were analyzed by HPLC to quantify HC-toxin. Results indicated a direct influence of nitrogen source and an absence of glucose catabolite repression. The accumulation of toxin was markedly increased by the addition of L-glutamine to the defined medium but inhibited by L-glutamate together with L-glutamine. L-Alanine and L-proline alone or in combination supported toxin production, but nitrate and ammonium as sole nitrogen sources did not. The potential effects of pH were discounted as major contributing factors. Relative to production in complex media, HC-toxin accumulated more rapidly but to lowe concentrations in the defined medium. The results suggest a role of amino acid regulation in the synthesis of this host-selective virulence factor.