Light-dependent accumulation of tryptamine in the rice Sekiguchi lesion mutant infected with Magnaporthe grisea

An antifungal compound with an infection-inhibiting activity was isolated from a rice Sekiguchi lesion (sl) mutant and identified as the indole alkaloid tryptamine. Tryptamine inhibited not only spore germination and appressorium formation of Magnaporthe grisea at high concentrations (> 600 mug/ml) but also the infection hypha formation in onion cells at low concentrations (150-300 mug/ml). Tryptamine is a normal compound of the rice sl-mutant but accumulates further in rice with a mutant-type response (Sekiguchi lesion formation) to inoculation with M. grisea spores. A mutant type of response is involved in light-enhanced resistance. The accumulation of tryptamine was not induced, however, in rice with a wild-type response (blast lesion formation). This study strongly suggests that tryptamine plays an important role as a possible factor in light-enhanced resistance in the rice sl-mutants.