Rice diterpenoid phytoalexins such as momilactones and phytocassanes are produced in suspension-cultured rice cells treated with a chitin oligosaccharide elicitor and in rice leaves irradiated with UV light. The common substrate geranylgeranyl diphosphate is converted into diterpene hydrocarbon precursors via a two-step sequential cyclization and then into the bioactive phytoalexins via several oxidation steps. It has been suggested that microsomal cytochrome P-450 monooxygenases (P-450s) are involved in the downstream oxidation of the diterpene hydrocarbons leading to the phytoalexins and that a dehydrogenase is involved in momilactone biosynthesis. However, none of the enzymes involved in the downstream oxidation of the diterpene hydrocarbons have been identified. In this study, we found that a putative dehydrogenase gene (AK103462) and two functionally unknown P-450 genes (CYP99A2 and CYP99A3) form a chitin oligosaccharide elicitor-and UV-inducible gene cluster, together with OsKS4 and OsCyc1, the diterpene cyclase genes involved in momilactone biosynthesis. Functional analysis by heterologous expression in Escherichia coli followed by enzyme assays demonstrated that the AK103462 protein catalyzes the conversion of 3␤-hydroxy-9␤H-pimara-7,15-dien-19,6␤-olide into momilactone A. The double knockdown of CYP99A2 and CYP99A3 specifically suppressed the elicitor-inducible production of momilactones, strongly suggesting that CYP99A2, CYP99A3, or both are involved in momilactone biosynthesis. These results provide strong evidence for the presence on chromosome 4 of a gene cluster involved in momilactone biosynthesis.Plants that are attacked by pathogenic microorganisms respond with a variety of defense reactions. One such reaction is the production of secondary metabolites that serve as plant antibiotics, known as phytoalexins, which are generated through the perception of signal molecules called elicitors, which are mostly derived from pathogens. Fifteen phytoalexin compounds have been identified in suspension-cultured rice cells treated with biotic elicitors such as a chitin oligosaccharide or a cerebroside (1, 2) and/or from rice leaves that were either infected with the rice leaf blast pathogen Magnaporthe grisea or exposed to UV irradiation (3-10). With the exception of the flavonoid sakuranetin, all of these rice phytoalexins are diterpenoids. These compounds have been classified into four structurally distinct types of polycyclic diterpenoid phytoalexins based on the structures of their diterpene hydrocarbon precursors: phytocassanes A to E, oryzalexins A to F, momilactones A and B, and oryzalexin S. The common precursor geranylgeranyl diphosphate is cyclized to ent-copalyl diphosphate (ent-CDP) and then to ent-cassa-12,15-diene and ent-sandaracopimaradiene, leading to phytocassanes A to E and oryzalexins A to F, respectively. Geranylgeranyl diphosphate is also cyclized to syn-CDP and then to 9␤H-pimara-7,15-diene and stemar-13-ene, leading to momilactones A and B and oryzalexin S, respectively. The hypotheti...

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The effect of CuO additions on the firing temperature of ZnNb 2 O 6 ceramics was investigated using dilatometry, transmission electron microscopy, and X-ray diffractometry. A 5 wt% CuO addition to ZnNb 2 O 6 ceramics significantly lowered the firing temperature from 1150°to ϳ900°C. The presence of a CuO-rich intergranular phase in the specimen was observed and was evidence of the formation of a liquid phase during sintering. The composition of the liquid phase was (ZnCu 2 )Nb 2 O 8 . In particular, the low-fired ZnNb 2 O 6 ceramics had good microwave dielectric characteristics-Q ؋ f ‫؍‬ 59 500, r ‫؍‬ 22.1, f ‫؍‬ -66 ppm/ o C. These properties were correlated with the formation of a second phase, (ZnCu 2 )Nb 2 O 8 .

The relationship between hydrophilicity and surface morphology of TiO2 film was investigated. TiO2 films were deposited by MOCVD, and anatase films were crystallized. The rougher the surface of anatase film, the slower the conversion from hydrophilic to hydrophobic state. Also in some films, even the sonication could not accelerate the kinetics. However, the recovery rate to hydrophilicity under UV illumination had a reverse dependency on the surface roughness. It was assumed that the rougher TiO2 films could have a large concentration of Ti 3+ generated by UV illumination on the surface, which plays a major role as adsorption sites of -OH in the water as well as in the air. Therefore, the healing kinetics of Ti 3+ by oxygen in the air of a dark room could have been different among films with various surface roughnesses. Conclusively, the sustaining tendency of hydrophilic or hydrophobic properties could mainly depend on the concentration of Ti 3+ by UV light, and in turn on the processing conditions of film deposition.