Silicon (Si) has been shown to play an important role in enhancing plant resistance against fungal pathogens. However, the mechanisms involved are still unclear. In this study, a series of experiments were performed to determine the effects of Si on resistance of rice to Magnaporthe oryzae infection. The rice mutant lsdm (leaf silicon-defective mutant), produced by Co-60 gamma-radiation treatment of wild type IR64, shows small yellow-brown spots at the three-leaf stage without pathogenic attack. Microscopic observation of lsdm leaves showed fractures of silica-phellem block, and Si content of leaf surface was lower than that of IR64 by 16.3. Disease reaction to M. oryzae indicated that the resistance of lsdm was reduced. Both IR64 and lsdm had a rapid but transient burst of hydrogen peroxide one day after inoculation, while catalase activity was suppressed. However, the lower catalase activity in the mutant did not affect the accumulation of hydrogen peroxide. The concentration of hydrogen peroxide had another minor peak at the fourth day after infection by M. oryzae. Malondialdehyde concentration and lipoxygenase activity were higher in the mutant, revealing more severe lipid peroxidation. Real-time fluorescence quantitative PCR was used to detect the expression of the phenylalanine ammonia-lyase (PAL), pathogenesis-related protein 1 (Pr1a), chitinase (Rcht) and catalase A (CatA) genes. The expression of all genes increased after inoculation. These results suggest that multiple rice M. oryzae resistance pathways might be influenced in lsdm plants.
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