Four Kinetic Phases Associated with the Fluorescence Induction Curve of DCMU-Poisoned Chloroplasts
The fluorescence induction curve obtained with dark-adapted chloroplasts inhibited with DCMU rises very rapidly to the Fo level and then more slowly to its maximum value, Fm. Early workers [1, 2] showed that the area above the fluorescence induction curve is proportional to the number of electron acceptors available to PS2 before the site of inhibition by DCMU. The rate at which this area is traced out reflects the reduction of these electron acceptors. The time taken for this process to occur will depend on the number of electron acceptors per reaction centre and the number of pigment molecules per reaction centre, which will determine respectively the amount of electrons to be transported and the frequency with which the reaction centre transports electrons. The concept of connectivity adds complexity to this interpretation. With connectivity, it is possible for excitons to escape from a closed, photosynthetic unit to an open unit. In effect this results in an increase in the number of pigment molecules per open reaction centre as electrons are transported and a continual increase in the rate constant.
KeywordsReaction Centre Electron Acceptor Pigment Molecule Kinetic Phasis Photosynthetic Unit
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