Influence of Ioxynil on the Photo-reduction of Endogenous Plastoquinone by Isolated Chloroplasts of Vicia faba L.

Abstract

ALTHOUGH plastoquinone (a 2,3-dimethyl p-benzoquinone, with a C45 side chain at C5) was first isolated in 1946 by Kofler from alfalfa grass, it did not excite much interest until Crane1 extracted the compound from the chloroplasts of green leaves. Plastoquinone (PQ) was first implicated as a participant in photosynthetic electron transport systems by Bishop2. Recently, Redfearn et al.3 have shown plastoquinone to be an intermediary electron carrier in the photosynthetic system, being a part of the light-dependent water-splitting mechanism as outlined by Duysens et al.4. We have recently reported5 that ioxynil (4-hydroxy-3,5-diiodo-benzonitrile)6 inhibits photophosphorylation and the accompanying reduction of pyridine nucleotide by chloroplasts. The results reported have been improved in recent months to give 50 per cent inhibition of both processes at a concentration of ioxynil of 5 × 10−5 M. In an attempt to elucidate the action of ioxynil on the photosynthetic electron transport system, the ability of chloroplasts to photo-reduce endogenous plastoquinone was investigated.

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References

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PATON, D., SMITH, J. Influence of Ioxynil on the Photo-reduction of Endogenous Plastoquinone by Isolated Chloroplasts of Vicia faba L.. Nature 207, 1211–1212 (1965). https://doi.org/10.1038/2071211b0

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