Measurements of cytochrome f and P-700 in intact leaves of Sinapis alba grown under high-light and low-light conditions |
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Authors: | W Rühle A Wild |
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Institution: | (1) Institut für Allemeine Botanik der Universität Mainz, Saarstraße 21, D-6500 Mainz, Federal Republic of Germany |
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Abstract: | The oxidation and reduction of cytochrome f and P-700 is measured spectrophotometrically in leaves of low-light and high-light plants. After illumination with red light, an induction phenomenon for cytochrome f oxidation is observed which indicates a regulation of photosystem I activity through energy distribution between the pigment systems by the energy state of the membrane. After far-red excitation the reduction of cytochrome f in the dark is much slower in low-light leaves. This shows that cyclic electron transport is not improved in low-light plants under these conditions. P-700 is oxidized on excitation with far-red light. However, with high intensities of far-red light, P-700 is partially reduced again which is due to a low extent of photosystem II excitation with the far-red used in the experiments. The low-light leaves show greater sensitivity of photosystem II to this excitation. The initial rate of the cytochrome f oxidation-rate is the same in low-light and high-light leaves. This shows that several P-700 are connected with only one electron transport chain. The consequences of these results concerning the tripartite concept and the photosynthetic unit are discussed. In the high-light plants the experimental data can be well explained by the tripartite organization of the photosynthetic unit. In low-light plants, however, a multipartite organization has to be postulated. In the partition regions of the grana, several antennae systems I, antennae systems II, and light-harvesting complexes can communicate with one electron transport chain.Abbreviations CP I
P-700-chlorophyll a-protein
- Cyt f
cytochrome f
- DCMU
3-(3,4 dichlorophenyl)-1,1-dimethylurea
- DBMIB
2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone
- LA
leaf-area
- PhAR
photosynthetically active radiation
- PS
photosystem |
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Keywords: | Cytochrome f Electron-transport High-light plants Low-light plants P-700 Photosynthetic unit |
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