Pyrenophora teres, the causal agent of net blotch of barley (Hordeum vulgare L.), induces distinctive long dark brown lesions (the net form) or dark brown spots (the spot form), both with surrounding chlorosis. Proteins isolated from P. teres f. teres (the net form) and P. teres f. maculata (the spot form) induce host-specific necrosis. In this study, the activity of these proteinaceous toxins was further characterised. The toxins were heat stable and their activity in planta was temperature and light dependent suggesting a role in targeting metabolically active and light-dependent organelles such as the chloroplast. In addition, proteinase K treatment after toxin treatment did not affect symptom induction by the toxins suggesting they are actively internalised. Adult barley plants were less sensitive to the toxins than younger plants, highlighting a potential adult resistance mechanism. Characterisation of these host-specific proteinaceous toxins produced by P. teres further assists our understanding of the role of such selective toxins in disease induction in plants. (C) 2008 Elsevier Ltd. All rights reserved.
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