Light‐Dependent Necrosis Formation by Magnaporthe grisea Toxin(s) in Rice cv. Sekiguchi‐asahi*

Abstract

The significance of light irradiation in neerosis formation by Magnaporthe grisea toxin(s) on rice cv. Sekiguchi‐asahi was investigated. The effective wave region for light‐dependent neerosis formation was 400 700 nm. An absorption band of the toxin(s) was restricted to the wave region shorter than 400 nm. Both of the phytosynthesis and necrosis formation were inhibited by photosynthetic inhibitors, and the inhibition of both activities was dependent on concentration of the inhibitors. The necrosis formation by the toxin(s) depended on light intensity. The toxin(s) induced the necrosis formation only on the cells with many chloroplasts, and the cells without chloroplasts did not form necrosis even under the light with sufficient intensity. The more the number of chloroplasts decreased, the more the size of necrotic spot decreased on the leaf sheath. From these results we concluded that the photosynthetic activity was involved in the necrosis formation by Magnaporthe grisea toxin(s) in rice cv. Sekiguchi‐asahi.

Light‐Dependent Accumulation of Tryptamine in the Rice Sekiguchi Lesion Mutant Infected with Magnaporthe grisea

“…6b). Previously, the present authors have demonstrated that the spore germination¯uid of M. grisea induced Sekiguchi lesion-like necrosis in a light-dependent manner (Arase et al, 1990b;Iedome et al, 1995). Tryptamine also accumulated in leaf necrosis induced by the spore germination¯uid under light, whereas it did not accumulate in the leaves where leaf necrosis formation was suppressed by dark treatment (data not shown).…”

“…Tryptamine also accumulated in leaf necrosis induced by the spore germination¯uid under light, whereas it did not accumulate in the leaves where leaf necrosis formation was suppressed by dark treatment (data not shown). However, neither tryptamine accumulation nor leaf necrosis was induced in leaves that were pretreated with the protein-and photosynthetic inhibitors cycloheximide and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) (Arase et al, 1993;Iedome et al, 1995), respectively, even under light (data not shown). Furthermore, tryptamine (600 lg/ml) induced Sekiguchi lesion-like necrosis in leaves of the rice sl-mutant under light.…”

Light‐Dependent Induction of Sekiguchi Lesion Formation by Bipolaris oryzae in Rice cv. Sekiguchi‐asahi

“…Investigations using the M. grisea ‐cv. Sekiguchi‐asahi system demonstrated that toxins produced by germinating spores of the pathogen played an important role as the primary inducer of Sekiguchi lesion formation ( Arase et al, 1990a,b; Iedome et al, 1995). Vidhyasekaran et al (1986) reported that B. oryzae produced a host‐specific toxin.…”

“…Light intensities were measured using a thermopile with a quartz window (MIR‐100Q, Mitsubishi Yuka Co., Ltd, Yokkaichi, Japan). Spectral energy distribution of the light sources and the filters' transmission ranges have been previously described ( Iedome et al, 1995).…”

Light‐Enhanced Resistance to Magnaporthe grisea Infection in the Rice Sekiguchi Lesion Mutants

“…Sekiguchi lesion‐like leaf necrosis has also been induced by treatment with various chemicals or with fungal toxins from germinating spores of M. grisea ( Kiyosawa, 1970; Arase et al, 1990a). Previous reports have demonstrated ( Arase et al, 1990b, 1997; Iedome et al, 1995) the significance of light irradiation in enhancing the formation of Sekiguchi lesion and necrosis in rice cv. Sekiguchi‐asahi.…”