Ca2+ and reactive oxygen species are involved in the defense responses of rice callus culture to rice blast disease

2+ and reactive oxygen species in the defense responses of callus cultures of rice (Oryza sativa L., cv. Zenith) to infection with avirulent strain of rice blast fungus (Magnaporthe grisea, strain Ina168) was investigated. It was observed that rice calli, especially after mild blast infection, exude substances (diffusate) that inhibit spore germination of the avirulent blast fungus. This fungitoxic calli diffusate led to superoxide dismutase-sensitive reduction of Nitro-blue-tetrazolium. Treatment of rice calli with crude elicitor from the blast fungus also led to hypersensitive necrotic response. Addition of antioxidant reagents diminishes the necrotic response of calli to the elictor treatment, implicating the involvement of reactive oxygen species in the hypersensitive necrotic response. When ethyleneglycoltetraacetic acid (Ca 2+ chelator) or LaCl3 (Ca 2+ channel blocker) was added, the necrotic response of calli to elicitor treatment was also significantly weakened, implying the involvement of Ca 2+