Tadami Akatsuka

Sakuranetin, a flavanone phytoalexin from ultraviolet-irradiated rice leaves

Abstract A new rice phytoalexin, sakuranetin (5,4′-dihydroxy-7-methoxyflavanone) was isolated from ultraviolet-irradiated rice leaves. The ED 50 value of sakuranetin against spore germination of Pyricularia oryzae was approximately 15 ppm. A marked incorporation of [ 14C ]phenylalanine into sakuranetin was observed in ultraviolet-irradiated rice leaves. Sakuranetin has also been observed in blast-infected rice leaves and the content in a resistant cultivar after infection with P. oryzae was much higher than in a susceptible cultivar.

Oryzalexin E, A diterpene phytoalexin from UV-irradiated rice leaves

Abstract The novel diterpene phytoalexin, oryzalexin E was isolated from UV-irradiated rice leaves. The structure and relative configuration of oryzalexin E wer

Antifungal melampolides from leaf extracts of Smallanthus sonchifolius

Abstract A new antifungal melampolide, 8-angeloyl-1(10),4,11(13)-germacuratrien-12,6-olid-14-oic acid methyl ester, named sonchifolin, as well as three known melampolides, polymatin B, uvedalin and enhydrin, were isolated from leaf extracts of Yacon [ Smallanthus sonchifolius (Poepp. and Endl.) H. Robinson]. Sonchifolin exhibited the highest fungicidal activity against Pyricularia oryzae , a fungus causing rice blast disease and the ED 50 value for the spore germination was 22 ppm. This is the first report of these melampolides as fungicidal compounds.

Oryzalexin S structure: a new stemarane-type rice plant phytoalexin and its biogenesis.

Abstract Details of the structural assignment of oryzalexin S, a novel rice plant phytoalexin obtained from 2-D NMR experiments, are presented. This is the first phytoalexin with the stemarane skeleton, and it indicates a characteristic biogenesis.

Oryzalexin S, a Novel Stemarane-type Diterpene Rice Phytoalexin

copper chloride6) and ultrayiolet irradiation.7) In panicular, ultraviolet irradiation is very convenient for the production and isolation of rice phytoalexins because it is easy to irradiate many rice leaves with ultraviolet light. Recently, we have found a new antifungal substance, whigh is distinct from the well-known rice phytoalcxins from ultravioletirradiated rice leaves.7) [n this report, we describe the isolation and structure elucidation procedures of the

Novel Phytoalexins (Oryzalexins A, B and C) Isolated from Rice Blast Leaves Infected with Pyricularia oryzae.

Oryzalexins A, B and C were isolated as a group of novel phytoalexins from rice (Oryza sativa) blast leaves infected with Pyricularia oryzae. The basis of the structures of Oryzalexins A, B and C was laid by spectroscopic methods and their inhibitory activities against spore germination and germ tube growth of P. oryzae were assayed.Oryzalexins A, B and C, isolated from rice leaves infected with P. oryzae as a group of novel phytoalexins, were confirmed to be (+)-sandaracopimaradiene derivatives by chemical and spectroscopic studies, i.e. A: 3-oxy-7-oxo- (I); B: 3-oxo-7-oxy- (II) and C: 3,7-dioxo-(+)-sandaracopimaradiene (III).

Mode of Action of Oryzalexin D against Pyricularia oryzae

The effect of oryzalexin D, which has been isolated as a group of novel phytoalexins of rice plant, on DNA, RNA, protein, lipid and chitin biosyntheses, respiration and cell membrane permeability was investigated in Pyricularia oryzae. The concentration for 50% inhibition (ED50) by oryzalexin D of the mycelial growth of P. oryzae was 230 ppm. At this concentration, oryzalexin D inhibited equally the incorporation of [2–14C]thymidine, [2–14C]uridine, l-[U-14C]amino acid mixture, l-[methyl-14C]methionine and d-[l-14C]glucosamine into DNA, RNA, protein, lipid and chitin in intact cells, but did not inhibit these systems in a homogenate of the mycelia of P. oryzae. Oryzalexin D scarcely inhibited the respiration of the homogenate and mitochondria at ED50. On the other hand, oryzalexin D at ED50 caused leakage of potassium and inhibited the uptake of glutamate by mycelial cells of P. oryzae. These results suggest that interference with the cell membrane function is responsible for the primary mode of action.of...

KITAZIN P AND EDIFENPHOS, POSSIBLE INHIBITORS OF PHOSPHATIDYLCHOLINE BIOSYNTHESIS

Abstract Of the two phosphatidylcholine biosynthetic pathways in Pyricularia oryzae , the biosynthesis of phosphatidylcholine by sequential methylations of phosphatidylethanolamine (Greenberg pathway) was inhibited by Kitazin P and edifenphos at the ED50 value for the mycelial growth of P. oryzae and the close correlation between growth inhibition and the inhibition of phosphatidylcholine biosynthesis via Greenberg pathway was observed. On the other hand, phosphatidylcholine biosynthesis from choline through CDP-choline (Kennedy pathway) was scarcely inhibited by Kitazin P and edifenphos. Phosphatidylcholine biosynthesis via the Kennedy pathway was strongly inhibited by hemicholinium-3, however, the mycelial growth was not influenced. Therefore, phosphatidylcholine biosynthesis via the Kennedy pathway was not essential for the mycelial growth of P. oryzae. No effects of Kitazin P and edifenphos on DNA, RNA, protein and chitin biosynthesis, and leakage in mycelia of P. oryzae were noted at the concentration of the ED50 value for mycelial growth. We conclude from the experimental results described that the primary antifungal action of Kitazin P and edifenphos is the inhibition of the phosphatidylcholine biosynthesis by transmethylation reaction.

A Mode of Action of Anti-blast Substances

The effects of organophosphorus fungicides, IBP (S-benzyl O, O-diisopropyl phosphorothiolate, Kitazin P®), EDDP (O-ethyl S, S-diphenyl phosphorodithiolate, edifenphos, Hinosan®) and ESBP (S-benzyl O-ethyl phenylphosphonothiolate, Inezin®) for Pyricularia oryzae were investigated. The fungicides did not significantly inhibited on DNA, RNA, protein and chitin biosynthesis, exogeneous respiration and leakage of potassium at the ED50 concentration value for mycelial growth. On the other hand, the close correlation between growth inhibition and the inhibition of phosphatidylcholine biosynthesis by sequential methylations of phosphatidylethanolamine (Greenberg pathway) was observed, but scarcely inhibited the biosynthesis of phosphatidylcholine from choline through CDP-choline (Kennedy pathway). Phosphatidylcholine biosynthesis via the Kennedy pathway was strongly inhibited by hemicholinium-3, however, the mycelial growth was not influenced. Therefore, phosphatidylcholine biosynthesis via the Kennedy pathway was not essential for the mycelial growth of P. oryzae. Thus, we conclude from the experimental results described that the primary antifungal action of organophosphorus fungicides is the inhibition of the phosphatidylcholine biosynthesis via the Greenberg pathway. Next, the degradation of IBP, EDDP and BPA (dibutyl N-methyl-N-phenylphosphoramidate) by P. oryzae, and the degradation of IBP by a pig liver reconstitution mixed function oxidase enzyme system were investigated. From the experimental results, we conclude the degradation of IBP, EDDP and BPA by mycelial cells of P. oryzae are catalyzed by mixed function oxidase. And next, we isolated a group of novel phytoalexins (Oryzalexin A, B and C) from rice plant (Oryza sativa) leaves infected with P. oryzae, and presented the absolute configurations of these substances as (+)-sandaracopimaradiene derivatives. Now, we are interested in the biosynthesis of Oryzalexins as to elucidate the dynamic aspect of plant protection.