Effect of metabolic inhibitors on red light-induced resistance of broad bean (Vicia faba L.) against Botrytis cinerea

A possible relationship between the synthetic activities of broad bean leaves and red light-induced resistance against Botrytis cinerea was examined. Both lesion formation and fungal development were suppressed under red light irradiation. In red light-irradiated leaflets, restricted chocolate lesions were observed only on their inoculated adaxial surfaces, whereas black lesion extended to non-inoculated abaxial surfaces in the dark. In microscopic studies, clear cell browning was recognized only in red light-irradiated leaves. Treatment of leaves with an inhibitor of photosynthesis, 3-(3,4-dichlorophenyl)-1,1-dimethyl urea ( DCMU) (25 muM), and an inhibitor of protein synthesis, cycloheximide (25 mug/ml), inhibited the induction of resistance by red light irradiation. Moreover, DCMU- and cycloheximide-treated lea et produced black necrotic lesion even under red light irradiation for 48 h, which extended to the non-inoculated abaxial surface. DCMU did not affect fungal growth, spore production or spore germination of B. cinerea. By contrast, cycloheximide at 25 mug/ml suppressed mycelial growth, but not spore production, whereas cycloheximide at the same concentration completely inhibited spore germination. These results suggest that red light-induced resistance possibly depends on host photosynthesis and protein synthesis.