Inhibition of Chloroplast Electron Transport Reactions by Trifluralin and Diallate 1

• Published in: Plant physiology (Bethesda) 1977-12, Vol.60 (6), p.840-844
• Main Authors: Robinson, Steven J., Yocum, Charles F., Ikuma, Hiroshi, Hayashi, Fumihiko
• Format: Article
• Language: English
• ISSN: 0032-0889; 1532-2548

The herbicides trifluralin (α,α,α-trifluoro-2,6-dinitro- N , N -dipropyl- p -toluidine) and diallate (S-[2,3-dichloroallyl] diisopropylthiocarbamate) inhibit electron transport, ATP synthesis, and cytochrome f reduction by isolated spinach ( Spinacia oleracea L.) chloroplasts. Both compounds inhibit noncyclic electron transport from H 2 O to ferricyanide more than 90% in coupled chloroplasts at concentrations less than 50 μ m . Neither herbicide inhibits electron transport in assays utilizing only photosystem I activity, and the photosystem II reaction elicited by addition of oxidized p -phenylenediamine or 2,5-dimethylquinone is only partially inhibited by herbicide concentrations which block electron flow from H 2 O to ferricyanide. Inhibition of ATP synthesis parallels inhibition of electron flow in all noncyclic assay systems, and cyclic ATP synthesis catalyzed by either diaminodurene or phenazine metho-sulfate is susceptible to inhibition by both herbicides. These results indicate that trifluralin and diallate both inhibit electron flow in isolated chloroplasts at a point in the electron transport chain between the two photosystems.