| Institution: | 1. Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501 Hyogo, Japan;2. AHS Agricultural Research and Extension Center, Virginia Polytechnic Institute and State University, Winchester, VA, 22655 USA;3. Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501 Hyogo, Japan
Graduate School of Engineering, Osaka University, Ibaraki, 567-0047 Osaka, Japan;4. National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba, 305-8604 Ibaraki, Japan |
| Abstract: | Hydrogen peroxide (H2O2) and lignin induced by acibenzolar-S-methyl (ASM) during the expression of systemic acquired resistance (SAR) of cucumber plants against the fungus Colletotrichum orbiculare was analysed with electron microscopy and energy-filtering electron microscopy (EFEM). ASM pretreatment consistently led to the blockage of appressorial penetration pegs into leaves at early stages after inoculation, whereas the fungus was able to grow into the vascular tissue after distilled water pretreatment. The blocked pegs, seen frequently at epidermal pectin layers in leaves of ASM-treated plants, were surrounded by abundant electron-dense amorphous material and dots. These were identified as lignin, based on their appearance and high reactivity with KMnO4. Lignin first appeared as an amorphous material at pectin layers, and then as dots in some areas of the material. The results showed that ASM caused SAR in leaves via faster formation of lignin within 1 day after inoculation. After CeCl3 treatment to detect H2O2, H2O2-reactive products (cerium perhydroxides) were seen near ASM-induced lignin formation sites in pectin layers. EFEM analysis showed that Ce and O were located at the same sites as the lignin dots, suggesting that lignin was associated with sources of H2O2 generation. The results indicate that the faster H2O2 generation and lignification induced by ASM were the potential causes of SAR. |
