Characterisation of low molecular weight phytotoxins isolated from Pyrenophora teres

We have previously shown that pooled low molecular weight compounds (LMWCs) isolated from culture filtrates of both forms of the barley net blotch pathogen Pyrenophora teres cause chlorosis. In this study, the LMWCs were further characterised and individually identified. The LMWCs were non-host selective compounds and their activity in planta was temperature and light-dependent suggesting a role in targeting metabolism and light-dependent organelles such as the chloroplast. Although the previously characterised toxins N-(2-amino-2-carboxyethyl) aspartic acid (Toxin A), 1-(2-amino-2-carboxyethyl)-6-carboxy-3-carboxymethyl-2-piperazinone (Toxin B), and N-[2-(2-amino-2-carboxy ethyl-amino)-2-carboxyethyl] aspartic acid (Toxin C) were identified, a number of other chlorosis-causing compounds were also isolated. Here, we report the first isolation of aspergillomarasmine B from P. teres media filtrates as well as the isolation and description of a unique u.v.-absorbing phytotoxic LMWC which appears to be a reductive conjugation of the α-keto acid of phenylalanine with Toxin A.