External electric field effects on photosynthetic membrane vesicles. Kinetic characterization of two electrophotoluminescence phases in hypotonically swollen chloroplasts |
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Authors: | Marc Symons Shmuel Malkin Rafi Korenstein |
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Institution: | 1. Department of Membrane Research, The Weizmann Institute of Science, Rehovot 76100 Israel;2. Department of Biochemistry, The Weizmann Institute of Science, Rehovot 76100 Israel |
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Abstract: | Strong externally applied electrical field pulses are known to stimulate delayed luminescence from preilluminated blebs (hypotonically swollen vesicles originating from thylakoid membranes of broken chloroplasts) by up to 3 orders of magnitude. This phenomenon is known as electrophotoluminescence. Previous analysis showed the kinetics of the electrophotoluminescence to be biphasic, displaying a rapid (R) phase which decays towards a slower one (S) (Ellenson, J.L. and Sauer, K. (1976) Photochem. Photobiol. 23, 113–123). We demonstrate that these two components represent different processes. At low pH, a good kinetic separation is obtained between the two phases, which become distinct, with the S phase manifesting also an initial rise period. Under these conditions, it is possible to estimate separately the approximate rise times of the two phases. It is shown that the R and S components have a different dependence on the pH and on the time between the actinic flash and onset of the field. The field dependence is also different, with the S phase requiring a lower threshold field than R. From these observations, it is concluded that the R and S luminescence components are formed by different precursors. The difference in behaviour of the two phases during formation of the bleb indicates that the precursors of the R and S phases belong to different parts of the bleb. We suggest that R precursors are located in the wall of the swollen thylakoid and S precursors in the membrane formations which are attached to this wall. |
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Keywords: | Electrophotoluminescence Membrane vesicle Thylakoid membrane Delayed luminescence Electric field effect (Lettuce spinach chloroplast) DCMU 3-(3-4-dichlorophenyl)-1 1-dimethylurea PS II Photosystem II |
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