Effect of encecalin, euparin and demethylencecalin on thylakoid electron transport and photophosphorylation in isolated spinach chloroplasts

• Published in: Journal of the science of food and agriculture Vol. 78; no. 1; pp. 102 - 108
• Main Authors: Castañeda, Perla, Mata, Rachel, Lotina-Hennsen, Blas
• Format: Journal Article
• Language: English
• Published: London John Wiley & Sons, Ltd 01-09-1998; Wiley; Published for the Society of Chemical Industry by Elsevier Applied Science
• Subjects: Asteraceae; benzofurane; benzopyrane; Biological and medical sciences; Chemical control; demethylencecalin; encecalin; energy-transfer inhibitor; euparin; Fundamental and applied biological sciences. Psychology; Helianthella quinquenervis; Parasitic plants. Weeds; photosynthesis; Phytopathology. Animal pests. Plant and forest protection; uncoupler; Weeds; Spinacia oleracea; Compositae; Pesticide crop; Thylakoid; Hill reaction; Electron transfer inhibitor; Photosystem 2; Dicotyledones; Angiospermae; Chemical control; Mechanism of action; Chloroplast; Photophosphorylation; Enzyme; Adenosinetriphosphatase; Pyran derivatives; Metabolic inhibitor; Herbicide; Phosphorylation inhibitor; Chenopodiaceae; Phytotoxicity; Vegetable crop; Plant origin; Hydrolases; Spermatophyta; Benzofuran derivatives; Photosynthesis
• ISSN: 0022-5142; 1097-0010
• DOI: 10.1002/(SICI)1097-0010(199809)78:1<102::AID-JSFA93>3.0.CO;2-I

The major phytotoxic compounds (encecalin, euparin and demethylencecalin) isolated from Helianthella quinquenervis (Hook) A Gray (Asteraceae) were evaluated on different photosynthetic activities in chloroplasts isolated from spinach leaves. ATP synthesis, proton uptake and electron flow (basal, phosphorylating and uncoupled) were inhibited by encecalin and demethylencecalin in a concentration dependent manner, therefore acting as Hill reaction inhibitors. Encecalin and demethylencecalin did not affect photosystem I (electron transport from diaminodurene to methylviologen), but they inhibited photosystem II (from water to 2,5‐dibromo‐3‐methyl‐6‐isopropyl‐1,4‐p‐benzoquinone). Since these compounds inhibited electron flow in the photosystem II partial reactions from water to silicomolybdate and from diphenylcarbazide to dichlorophenol‐indophenol, the site of inhibition was located in the span from P680 to QA of the electron transport chain. Euparin, inhibited ATP synthesis, proton uptake and basal and phosphorylating electron transports, but it has not effect on uncoupled electron flow from water to methylviologen. Mg2+‐ATPase activity from bound membrane thylakoid chloroplasts was also inhibited by this compound. These results suggested that euparin inhibited phosphorylation in chloroplasts, acting as an energy‐transfer inhibitor. © 1998 Society of Chemical Industry.