SummaryThe upregulation of the tryptophan (Trp) pathway in rice leaves infected by Bipolaris oryzae was indicated by: (i) enhanced enzyme activity of anthranilate synthase (AS), which regulates metabolic flux in the Trp pathway; (ii) elevated levels of the AS (OASA2, OASB1, and OASB2) transcripts; and (iii) increases in the contents of anthranilate, indole, and Trp. The measurement of the contents of Trp-derived metabolites by highperformance liquid chromatography coupled with tandem mass spectrometry revealed that serotonin and its hydroxycinnamic acid amides were accumulated in infected leaves. Serotonin accumulation was preceded by a transient increase in the tryptamine content and by marked activation of Trp decarboxylase, indicating that enhanced Trp production is linked to the formation of serotonin from Trp via tryptamine. Feeding of radiolabeled serotonin to inoculated leaves demonstrated that serotonin is incorporated into the cell walls of lesion tissue. The leaves of a propagating-type lesion mimic mutant (sl, Sekiguchi lesion) lacked both serotonin production and deposition of unextractable brown material at the infection sites, and showed increased susceptibility to B. oryzae infection. Treating the mutant with serotonin restored deposition of brown material at the lesion site. In addition, the serotonin treatment suppressed the growth of fungal hyphae in the leaf tissues of the sl mutant. These findings indicated that the activation of the Trp pathway is involved in the establishment of effective physical defenses by producing serotonin in rice leaves.

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The electronic structural changes of La0.6Sr0.4CoO3−δ cathodes with oxygen vacancy formation by reducing oxygen partial pressures, p(O2)'s were investigated in detail using X-ray absorption spectroscopy to understand metallic-like electronic conduction mechanism. The oxygen nonstoichiometry of La0.6Sr0.4CoO3−δ was controlled by annealing the samples under various p(O2)'s and quenched to room temperature. Co K-edge X-ray absorption near edge structure (XANES) spectra revealed that the Co average valence decreased with decreasing p(O2), which was also confirmed by iodometric titration. The Co L-edge XANES spectra were hardly changed with changing p(O2)'s. Meanwhile, the peak area of the O K-edge XANES spectra strongly depended on p(O2). This result revealed the strong hybridization between the O 2p and Co 3d states. It was concluded the introduction of oxygen vacancies narrowed the hybridized orbital of O 2p and Co 3d states, resulted in a decrease in the mobility as well as the concentration of electron holes with decreasing p(O2).

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Highly dense pellets of an oxygen excess-type lanthanum silicate ͑La 9.333+x Si 6 O 26+1.5x , x Ͼ ca. 0.3, OE-LSO͒ were successfully fabricated, and their electrical conducting properties were studied. The replacement of Si by Al enhanced its conductivity, and the slightly Al-doped OE-LSO specimen ͓La 9.62 ͑Si 5.79 Al 0.21 ͒O 26.33 ͔ had excellent features as a solid electrolyte; that is, it had high ionic conductivity and was highly stable under reducing as well as oxidizing conditions at 873-1073 K. In addition, the ionic transference number was higher than 0.99. In the fuel cell utilizing this electrolyte ͑0.72 mm thick͒, ͑La 0.6 Sr 0.4 ͒͑Co 0.2 Fe 0.8 ͒O 3−␦ cathode, and Ni-Ce 0.9 Gd 0.1 O 1.95−␦ anode, good performance with the maximum power density of ca. 0.25 W cm −2 was obtained at 1073 K. In addition, this electrolyte also had high compatibility with these conventional mixed conducting electrodes, according to an analysis near the electrode/electrolyte interfaces after the fuel cell test.Solid oxide fuel cells ͑SOFCs͒ attract much attention as commercial or household energy conversion devices capable of producing heat as well as electricity directly from natural gas. Because they exhibit high energy efficiency compared with present energy conversion systems, it is expected that developing practical fuel cells will give us a gift for the next generation, encouraging a sustainable use of resources and reducing carbon dioxide emission. In SOFCs, oxide ion or proton conducting oxide ceramics materials are employed as electrolytes. Well-known zirconia-based oxide ion conductors, such as yttria-stabilized zirconia ͑YSZ͒, have long been used as electrolyte materials for SOFCs, but are just now entering the long-awaited stage of practical application.Cost, however, presents a problem. One of the reasons for this is the necessity of using high cost heat-resistive interconnecting materials available for a high operating temperature of around 1273 K. Fuel cell reliability is also a problem due to poor mechanical strength of the electrolyte during operation at such a high temperature or during startup/shutdown cycles. Because of the high activation energy for the ionic conduction of YSZ ͑ca. 0.9 eV͒, its good ionic conductivity ͑ca. 10 −1 S cm −1 at 1273 K͒ falls to ca. 10 −2 S cm −1 at 973 K. If one could develop a novel solid electrolyte that conducts ions sufficiently ͑above 10 −1 S cm −1 ͒ in a reducing temperature region ͑773-1073 K͒, then less expensive stainless steel could be used for the surrounding materials of fuel cells. Hence, there is an escalating need for developing solid electrolytes for this temperature region to improve reliability as well as reduce cost.Oxide ion conduction through material based on lanthanum silicate ͑La 9.333+x Si 6 O 26+1.5x , LSO͒ with apatite-type structure, shown in Fig. 1, was originally discovered by Nakayama et al. 1,2 in 1995. This material is notable because of its low activation energy for conduction, while the reported ionic conductivity was about 10 −3 S cm −1 at 97...

The electrical conduction mechanism of mixed conductive perovskite oxides, La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ), for cathode materials of solid oxide fuel cells has been investigated from electronic structural changes during oxygen vacancy formation. La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) was annealed under various oxygen partial pressures p(O(2))s at 1073 K and quenched. Iodometric titration indicated that the oxygen nonstoichiometry of La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) depended on the annealing p(O(2)), with more oxygen vacancies introduced at lower than at higher p(O(2))s. X-Ray absorption spectroscopic measurements were performed at the O K-, Co L-, Fe L-, Co K-, and Fe K-edges. The valence states of the Co and Fe ions were investigated by the X-ray absorption near edge structure (XANES) at the Co and Fe L(III)-edges. While the Fe average valence was almost constant, the valence of the Co ions decreased with oxygen vacancy introduction. The O K-edge XANES spectra indicated that electrons were injected into the Co 3d/O 2p hybridization state with oxygen vacancy introduction. Both absorption edges at the Co and Fe K-edge XANES shifted towards lower energies with oxygen vacancy introduction. The shift at the Co K-edge resulted from the decrease in the Co average valence and that at the Fe K-edge appeared to be caused by changes in the coordination environment around the Fe ions. The total conductivity of La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) decreased with decreasing p(O(2)), due to a decreasing hole concentration.