| | 2 | Author
| StuartM. Ridley, Peter Horton | Requires cookie* | | | Title
| DCMU-Induced Fluorescence Changes and Photodestruction of Pigments Associated with an Inhibition of Photosystem I Cyclic Electron Flow  | | | | Abstract
| Diuron (DCM U) induces the photodestruction o f pigm ents, w hich is the initial herbicidal symptom. As a working hypothesis, it is proposed that this sym ptom can only be produced when the herbicide dose is sufficiently high to inhibit not only photosystem II electron transport alm ost completely, but also inhibit (through over oxidation) the natural cyclic electron flow associated with photosystem I as well. Using freshly prepared chloroplasts, studies o f D C M U -induced fluorescence changes, and dose responses for inhibition o f electron transport, have been com pared with a dose response for the photodestruction o f pigm ents in chloroplasts during 24 h illumination. Photodestruction o f pigm ents coincides with the inhibition o f cyclic flow. | | | |
Reference
| Z. Naturforsch. 39c, 351 (1984); received October 10 1983 | | | |
Published
| 1984 | | | |
Keywords
| Diuron (DCM U), Photodestruction, Fluorescence, Photosystem I, Cyclic Electron Flow | | | |
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| default:Reihe_C/39/ZNC-1984-39c-0351.pdf | | | | Identifier
| ZNC-1984-39c-0351 | | | | Volume
| 39 | |
| 3 | Author
| G. Renger, R. H. Agem Ann, W.F J V Erm Aas | Requires cookie* | | | Title
| Studies on the Functional Mechanism of System II Herbicides in Isolated Chloroplasts | | | | Abstract
| The effect o f specific proteolytic enzymes on variable fluorescence, p-benzoquinone-m ediated oxygen evolution, PS II herbicide (atrazine and brom oxynil) binding, and protein degradation has been analyzed in isolated class II pea chloroplasts. It was found that: 1. Trypsin and a lysine-specific protease effectively reduce the m axim um chlorophyll-a flu o rescence yield, whereas the initial fluorescence remains alm ost constant. At the sam e number o f enzymatic activity units both proteases have practically the sam e effect. 2 Trypsin and a lysine-specific protease inhibit the /»-benzoquinone-m ediated flash-induced oxygen evolution with trypsin being markedly more effective at the sam e num ber o f activity units o f both enzymes. Unstacked thylakoids exhibit a higher sensitivity to proteolytic degrada tion by both enzymes. 3. Trypsin and a lysine-specific protease reduce the binding capacity o f [14C]atrazine, but enhance that o f [l4C]bromoxynil (at long incubation tim es trypsin treatm ent also impairs bromoxynil binding). At the same specific activity a m arkedly longer treatm ent is required for the lysine-specific protease in order to achieve the same degree o f m odification as w ith trypsin. 4. Trypsin was found to attack the rapidly-turned-over 32 kD a-protein severely, whereas the lysine-specific protease does not m odify this polypeptide. On the other hand, the lysine-specific protease attacks the light harvesting com plex II. 5. Under our experimental conditions an arginine-specific protease did not affect chlorophyll-a fluorescence yield, /?-benzoquinone-mediated oxygen evolution, herbicide binding and the p oly peptide pattern. Based on these results a m echanism is proposed in w hich an as yet unidentified polypeptide with exposable lysine residues, as well as the lysine-free "Q B-protein" regulate the electron transfer from Q ^ to Q B and are involved in herbicide binding. | | | |
Reference
| Z. Naturforsch. 39c, 362—367 (1984); received Decem ber 1 1983 | | | |
Published
| 1984 | | | |
Keywords
| Chloroplasts, Proteolytic Enzymes, Fluorescence, Oxygen Evolution, H erbicide Binding | | | |
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| default:Reihe_C/39/ZNC-1984-39c-0362.pdf | | | | Identifier
| ZNC-1984-39c-0362 | | | | Volume
| 39 | |
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