A study of dark luminescence in Chlorella. Background luminescence, XXXX -triggered luminescence and hydrogen peroxide chemiluminescence.

@entity11079 @entity26 @entity274 @entity14786
Dark luminescence, defined as the ability of completely relaxed (dark-adapted) photosynthetic systems to emit light, has been studied in Chlorella. Three main effects have been demonstrated. @entity11079 elicits a weak emission LD of very long lifetime (several minutes); it is believed to result from a negative shift of redox potential of the secondary System II electron acceptor B producing in some centers a state Q- (reduced primary acceptor), as postulated by Velthuys and Amesz ((1974 Biochim. Biophys. Acta 333, 85--94), which can recombine with an oxidizing equivalent in a state S2 present in very small amount. As in photoinduced luminescence, this recombination excites chlorophyll which then emits light. A much stronger emission LH is observed after injection of @entity274 . Both signals are modified or suppressed by treatments specific of the @entity26 emission system, such as: thermal denaturation at 50 degrees C, @entity14786 , etc. In addition, a weak, permanent background luminescence L0 has been observed; like LD and and LH, it is a System II property and requires the integrity of the @entity26 -evolving system. It is believed to reflect a very slow back flow of electrons from an endogeneous reductant pool to @entity26 through part of the photosynthetic chain. Using flash preillumination, it is demonstrated that @entity274 is able to oxidize S0 into S2, the latter giving rise to LH; @entity274 does not act on S1 (or much less). The reactive site of @entity274 seems to be the same as the binding site of @entity14786 . Evidence is given that the strong LH signal in particular reveals a stable, low pH of the intrathylakoid phase in Chlorella.
