Biochemical studies on Cochliobolus miyabeanus. III.

Abstract

The resistance of the leaf-sheath cells of rice plants against Cochliobolus miyabeanus was markedly decreased by adding reducing agents, such as ascorbate or glutathione, to the inoculum.Phytoalexin-like antifungal substance was produced as a result of interaction between the cells of rice plants and the germinating spores of C. miyabeanus. However, since ascorbate and glutathione did not either decrease the activity of phytoalexin, or did not inhibit the formation of such a substance, the active principle in resistance which was inactivated by adding reducing agents would not be referred to the activity of phytoalexin.The invaded cells of leaf-sheath and their neighbouring cells were oxidatively stained with various rH indicators at the begining of hyphal penetration. It is noticeable that the parts of mycelia which were in contact with the membranes of inner epidermal cells of the leaf-sheath were also oxidatively stained in deep colour. The invaded cells of the resistant variety, Kameji, were stained with methylene blue in green colour at the begining of invasion, while in the susceptible variety, Asahi, the colour reaction was nearly blue.Judging from these results, it was concluded that the resistance of rice plant against hyphal penetration of C. miyabeanus is, to some extent, attributable to the fungal oxidation products, perhaps quinones, which are derived from the host cells or membranes.