Cooperativity between Photosystem II centers at the level of primary electron transfer |
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Authors: | Bruce Diner |
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Affiliation: | Laboratoire de Photosynthèse, Institut de Biologie Physico-Chimique, 13, rue Pierre et Marie Curie, 75231, Paris 05, France |
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Abstract: | 1. Spinach chloroplasts, but not whole Chlorella cells, show an acceleration of the Photosystem II turnover time when excited by non-saturating flashes (exciting 25 % of centers) or when excited by saturating flashes for 85–95 % inhibition by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Following dark adaptation, the turnover is accelerated after a non-saturating flash, preceded by none or several saturating flashes, and primarily after a first saturating flash for 3-(3,4-dichlorophenyl)-1,1-dimethylurea inhibition. A rapid phase ( approx. 0.75 s) is observed for the deactivation of State S2 in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea.2. These accelerated relaxations suggest that centers of Photosystem II are interconnected at the level of the primary electron transfer and compete for primary oxidizing equivalents in a saturating flash. The model in best agreement with the experimental data consists of a paired interconnection of centers.3. Under the conditions mentioned above, an accelerated turnover may be observed following a flash for centers in S0, S1 or S2 prior to the flash. This acceleration is interpreted in terms of a shift of the rate-limiting steps of Photosystem II turnover from the acceptor to the donor side. |
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Keywords: | DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea CMU |
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