CHANGES IN DIHYDROXYMETHOXYBENZOXAZINONE GLYCOSIDE CONTENT IN WHEAT PLANTS INFECTED BY 3 PLANT-PATHOGENIC FUNGI

Hydroxamic acids (Hx), present among members of the family Gramineae, defend the plant against several insect species and some bacteria. The ir role in defence against Fungal pathogens is still unclear. We teste d the hypothesis that the mode of infection by the fungus influences t he release from DIMBOA-glucoside, the main Hx in wheat, of the more ac tive aglycone DIMBOA. Infection by the pathogenic necrotroph Septoria tritici resulted in significant hydrolysis of DIMBOA-glucoside in seed lings of two wheat cultivars differing in Hx concentrations. Infection by Drechslera teres, a necrotroph non-compatible with wheal but patho genic on barley, caused only a slight reduction of glucoside concentra tion. The content of aglycone did not increase concurrently in any of these experiments. No change in glucoside content was evident followin g infection by the obligate parasite Puccinia recondita. In vitro, S. tritici was able to increase by 39% the rate at which DIMBOA disappear ed from aqueous solutions. Free DIMBOA was not detected in roots of pl ants infected with S. tritici, but there was a tendency for glucoside levels to be higher than in roots of control plants. (C) 1995 Academic Press Limited