title: Siderin from Toona ciliata (Meliaceae) as photosystem II inhibitor on spinach thylakoids.
abstract: Four natural products were isolated from plants of the Rutaceae and Meliaceae families and their effect on photosynthesis was tested. Siderin (1) inhibited both ATP synthesis and electron flow (basal, phosphorylating, and uncoupled) from water to methylviologen (MV); therefore, it acts as Hill reaction inhibitor in freshly lysed spinach thylakoids. Natural products 2-4 were inactive. Secondary metabolite 1 did not inhibit PSI electron transport. It inhibits partial reactions of PSII electron flow from water to 2,6-dichlorophenol indophenol (DCPIP), from water to sodium silicomolybdate, and partially inhibits electron flow from diphenylcarbazid (DPC) to DCPIP. These results established that the site of inhibition of 1 was at the donor and acceptor sides of PSII, between P(680) and Q(A). Chlorophyll a fluorescence measurements confirmed the behavior of the Toona ciliate coumarin 1 as P(680) to Q(A) inhibitor by the creation of silent centers. May be this is the mechanisms of action of 1 and is the way in which it develops a phytotoxic activity against photosynthesis.
authors.affiliation: Departamento de Química, Universidade Federal de São Carlos (UFSCar), 13565-905, São Carlos, S.P., Brazil.
authors.forename: Thiago A M
authors.initials: TA
authors.lastname: Veiga
authors.forename: Raquel
authors.initials: R
authors.lastname: González-Vázquez
authors.forename: João Oiano
authors.initials: JO
authors.lastname: Neto
authors.forename: Maria F G F
authors.initials: MF
authors.lastname: Silva
authors.forename: Beatriz
authors.initials: B
authors.lastname: King-Díaz
authors.forename: Blas
authors.initials: B
authors.lastname: Lotina-Hennsen
mesh_terms: D003374:Coumarins / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D008027:Light; D029582:Meliaceae / Q000737:chemistry*; D010788:Photosynthesis / Q000187:drug effects / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000037:antagonists & inhibitors*; D010936:Plant Extracts / Q000008:administration & dosage; D018724:Spinacia oleracea / Q000502:physiology*; D020524:Thylakoids / Q000737:chemistry / Q000502:physiology* / Q000528:radiation effects
chemical_list: D003374:Coumarins; D045332:Photosystem II Protein Complex; D010936:Plant Extracts