title: Effect of phytotoxic secondary metabolites and semisynthetic compounds from endophytic fungus Xylaria feejeensis strain SM3e-1b on spinach chloroplast photosynthesis.
abstract: We investigated the mechanism of action on the photosynthesis light reactions of three major secondary metabolites produced by the endophytic fungus Xylaria feejeensis strain SM3e-1b, isolated from Sapium macrocarpum; and four novel derivatives of coriloxine, a major compound produced by X. feejeensis. The natural phytotoxins include one epoxycyclohexenone derivative, coriloxine (1), and two quinone derivatives (2-3). The semisynthetic derivatives of coriloxine are two cyclohexenone (4-6) and two quinone compounds (5-7). Cyclohexenone (4), (4R,5S,6R)-6-chloro-4,5-dihydroxy-3-methoxy-5-methylcyclohex-2-enone, inhibited ATP synthesis in freshly lysed spinach chloroplasts from water to MV; it also partly inhibited the basal and uncoupled photosynthetic electron transport, and significantly enhanced the phosphorylating electron transport and Mg2+-ATPase activity, thus demonstrating its action as an uncoupler agent. On the other hand, quinone (7), 2-((4-butylphenyl)amino)-5-methoxy-3-methylcyclohexa-2,5-diene-1,4-dione, inhibited ATP synthesis, and non-cyclic electron transport from water to MV in basal, phosphorylating and uncoupled conditions in a concentration-dependent manner. Hence, (7) behaves as a Hill reaction inhibitor at the PSII electron transport on the water splitting enzyme (OEC), and on the acceptor side between P680and QA. This mechanism of action was confirmed by chlorophyll a fluorescence measurements. These results indicate that coriloxine derivatives 4 and 7 could work as prototype structures for the development of new herbicides. Contrastingly, natural products 1-3, and derivatives 5 and 6 did not show a significant inhibitory effect on ATP synthesis.
authors.affiliation: Instituto de Química, Departamento de Productos Naturales, Universidad Nacional Autónoma de México (UNAM), Ciudad Universitaria, Coyoacán, Ciudad de México 04510, Mexico. Electronic address: mmacias@iquimica.unam.mx.
authors.forename: Martha Lydia
authors.initials: ML
authors.lastname: Macías-Rubalcava
authors.affiliation: Instituto de Química, Departamento de Productos Naturales, Universidad Nacional Autónoma de México (UNAM), Ciudad Universitaria, Coyoacán, Ciudad de México 04510, Mexico.
authors.forename: Marbella Claudia
authors.initials: MC
authors.lastname: García-Méndez
authors.affiliation: Facultad de Química, Departamento de Bioquímica, Universidad Nacional Autónoma de México (UNAM), Ciudad Universitaria, Coyoacán, Ciudad de México 04510, Mexico.
authors.forename: Beatriz
authors.initials: B
authors.lastname: King-Díaz
authors.affiliation: Facultad de Química, Departamento de Fisicoquímica, Universidad Nacional Autónoma de México (UNAM), Ciudad Universitaria, Coyoacán, Ciudad de México 04510, Mexico.
authors.forename: Norma Angélica
authors.initials: NA
authors.lastname: Macías-Ruvalcaba
mesh_terms: D001203:Ascomycota / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D004579:Electron Transport; D010788:Photosynthesis; D018724:Spinacia oleracea / Q000378:metabolism*
keywords: Coriloxine; Cyclohexenone derivative; Endophytic fungi; Hill reaction inhibitors; Photosynthetic activities; Phytotoxic compounds; Quinone derivative; Sapium macrocarpum; Uncoupler agents; Xylaria feejeensis