FLUORESCENCE INDUCTION IN ALGAE AND CHLOROPLASTS |
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Authors: | Jerome Lavergne |
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Affiliation: | Laboratoire de Photosynthèse du C.N.R.S., 91190 Gif-sur-Yvette, France |
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Abstract: | Abstract —The first phases of the fluorescence transient elicited by illumination of dark-adapted algae or isolated chloroplasts (biphasic rise φ***v - φI - P) have previously been shown to be controlled by two quenchers: Q , the primary acceptor of Photosystem 2 interacting with the secondary acceptor pool A ; and R , a non-photochemical quencher which goes into a non-quenching state as A is reduced. The dependence of the kinetics of φ decay after illumination upon the redox state of A was studied. It is suggested that some of the centres are in a disconnected state, where electron transfer between Q and A is hindered, the amount of such centres being correlated to the reduction state of A . The implications of this hypothesis on the problem of the variation of the Q-A 'equilibrium constant' under different experimental conditions, and on Murata's 'weak light effect' are discussed. The effect of 3-(3,4 dichlorophenyl)-1,1 dimethylurea (DCMU) on R is shown to depend upon the redox state of A . A DCMU-induced shift of the midpoint potential of R may account for this dependence. Evidence is given suggesting that the transient reduction of A which occurs in algae during the φI-φP rise is controlled by an induction process on the acceptor side of Photosystem 1. |
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