Interference of l, 2, 3, 4-Tetramethoxy-5-(2-propenyl)benzene with Photosynthetic Electron Transport

The effect of 1,2,3,4-tetramethoxy-5-(2-propenyl)benze ne, the major phytogrowth-inhibitory agent iso lated from the leaves, stem bark and wood of Malmea depressa (Annonaceae), on seve ral photosynthetic acti vities has been investiga ted using freshly Iysed spin ach ch loroplasts. The res ults indicate that this compound inhibits proton-uptake, ATP synthesis and electron f10w (basal , ph osphorylatin g and uncoupled)in a concentration dependen! manner, th erefore acting as a Hill reaction inhibitor. Uncoupled electron transpo rt through photosystem I from red uced dichlorophenol-i ndophenol to meth ylviologen is unaffected by this compound. On the other hand, uncoupled electron transpo rt through photosystem Il from water to dichlorophenol-indophenol, from water to silicomolibdate and from diphenylcarbazide to dichlorophenol-indophenol is inhibited by this phenylpropanoid , suggesting th at th e site of inhibition is located in the span from P680 to QA'