African Journal of Biotechnology Vol. 3 (1), pp. 76-81, January 2004

Full Length Research Paper

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

Kuta D.D.* and Gaivaronskaya L.M.

Laboratory of Agrobiotechnology, Department of Plant physiology and Botany, Faculty of Agriculture, People Friendship University of Russia, Moscow, Russia.

*Corresponding author. Current address: Biotechnology Advanced Laboratory, Sheda Science and Technology Complex (SHESTCO), PMB 186 Garki, Abuja, Nigeria. E-mail: drkuta2002@yahoo.com.

Accepted 6 December 2003

The role of Ca²⁺ 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 (Ca²⁺ chelator) or LaCl₃ (Ca²⁺channel blocker) was added, the necrotic response of calli to elicitor treatment was also significantly weakened, implying the involvement of Ca²⁺ in the defense response.

Key words: Oryza sativa, Magnaporthe grisea, hypersensitive response, reactive oxygen species, calcium.