Abstract
We have analyzed the binding of synthetic quinones and herbicides which inhibit electron transport at the acceptor side of Photosystem II (PS II) of the photosynthetic electron-transport chain in thylakoid membranes. These data show that quinones and PS II-directed herbicides compete for binding to a common binding environment within a PS II region which functions as the Q- PQ oxidoreductase. We observed that (1) synthetic quinones cause a parallel inhibition of electron transport and [14C]herbicide displacement, and (2) herbicide binding is affected both by the fully oxidized and fully reduced form of a quinone. Quinone function and inhibitor binding were also investigated in thylakoids isolated from triazine-resistant weed biotypes. We conclude the following. (1) The affinity of the secondary accepting quinone, B, is decreased in resistant thylakoids. (2) The observation that the equilibrium concentration of reduced Q after transferring one electron to the acceptor side of PS II is increased in resistant as compared to susceptible chloroplasts may be explained both by a decrease in the affinity of PQ for the herbicide / quinone binding environment, and by a decrease of the midpont redox potential of the B B- couple. (3) The binding environment regulating quinone and herbicide affinity may be divided roughly into two domains; we suggest that the domain regulating quinone head-group binding is little changed in resistant membranes, whereas the domain-regulating quinone side-group binding (and atrazine) is altered. This results in increased inhibitory activity of tetrachloro-p-benzoquinone and phenolic herbicides, which are hypothesized to utilize the quinone head-group domain. The two domains appear to be spatially overlapping because efficient atrazine displacement by tetrachloro-p-benzoquinone is observed.
Original language | English (US) |
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Pages (from-to) | 483-491 |
Number of pages | 9 |
Journal | BBA - Bioenergetics |
Volume | 725 |
Issue number | 3 |
DOIs | |
State | Published - Dec 30 1983 |
Externally published | Yes |
Keywords
- Electron transport
- Herbicide
- Photosystem II
- Plastoquinone
- Quinone
- Thylakoid membrane
ASJC Scopus subject areas
- Biophysics
- Biochemistry
- Cell Biology