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Silicon-Induced Cell Wall Fortification of Rice Leaves: A Possible Cellular Mechanism of Enhanced Host Resistance to Blast

First and third authors: School of Agricultural Biotechnology, Seoul National University, Suwon 441-744, Korea; second author: National Instrumentation Center for Environmental Management, Seoul National University, Suwon 441-744, Korea; and fourth author: Korea Research Institute of Bioscience and Biotechnology, Taejon, 305-333, Korea

Locations of silicon accumulation in rice leaves and its possible association with resistance to rice blast were investigated by electron microscopy and X-ray microanalysis. A blast-susceptible cultivar, Jinmi, and a partially resistant cultivar, Hwaseong, were grown under a hydroponic culture system with modified Yoshida's nutrient solution containing 0, 50, 100, and 200 ppm of silicon. Electron-dense silicon layers were frequently found beneath the cuticle in epidermal cell walls of silicon-treated plants. Increasing levels of silicon were detected in the outer regions of epidermal cell walls. Silicon was present mainly in epidermal cell walls, middle lamellae, and intercellular spaces within subepidermal tissues. Furthermore, silicon was prevalent throughout the leaf surface, with relatively small deposition on stomatal guard cells in silicon-treated plants. Silicon accumulation and epidermal cell wall thickness in leaves were greater in cv. Jinmi than in cv. Hwaseong. However, the thickness ratios of the silicon layers to epidermal cell walls were greater in cv. Hwaseong (53.25 to 93.28%) than in cv. Jinmi (36.58 to 66.54%). Leaf blast severity was lower in cv. Hwaseong than in cv. Jinmi and was significantly reduced in silicon-treated plants of both cultivars. These results suggest that silicon-induced cell wall fortification of rice leaves may be closely associated with enhanced host resistance to blast.

Additional keywords: analytical electron microscopy, host defense, Magnaporthe grisea, mineral nutrition, Oryza sativa.