PRODUCTION OF A PROTEINACEOUS PHYTOTOXIN BY ASCOCHYTA-RABIEI GROWN INEXPRESSED CHICKPEA SAP

Production of the solanapyrone toxins by Ascochyta rabiei is nutrient dependent. When grown on a medium consisting entirely of expressed sap from the aerial parts of young chickpea plants (PSM), only low concen trations of the solanapyrones were produced (<24 mu M). However, toxic ity of 4-day-old culture filtrates to isolated cells of chickpea leafl ets was comparable with that obtained from 12-day-old culture filtrate s on Czapek Dox nutrients supplemented with chickpea seed extract or c ations-media that are conducive to solanapyrone production. The additi onal toxic component which peaked at 4 days in culture was heat labile , losing about 50% of its activity on boiling for 10 min. Affinity for solid-phase extraction media, precipitation with ammonium sulphate an d acetone, ionization properties and UV absorption characteristics sug gested that the toxin was a polypeptide. The toxin was purified by sol id-phase extraction, acetone precipitation and high performance liquid chromatography (HPLC) on a C2 column. Hydrolysis of the purified toxi n yielded 14 amino acids, and calculation of the numbers of residues o f each amino acid suggested a molecular mass of 7,551 Da. A band corre sponding to this molecular mass was present on SDS-PAGE gels. However, both the native peptide and its hydrolysate contained a compound that reacted with p-anisaldehyde suggesting the possibility of a glycosidi c moiety.