Redox changes accompanying inorganic carbon limitation in XXXX .

@entity3883 @entity324
UNASSIGNED: Inorganic carbon (Ci) is the major sink for photosynthetic reductant in organisms capable of oxygenic photosynthesis. In the absence of abundant Ci, the cyanobacterium @entity324 expresses a high affinity Ci acquisition system, the @entity3883 ( @entity3883 ), controlled by the transcriptional regulator CcmR and the metabolites NADP(+) and a-ketoglutarate, which act as co-repressors of CcmR by modulating its DNA binding. The @entity3883 thus responds to internal cellular redox changes during the transition from Ci-replete to Ci-limited conditions. However, the actual changes in the metabolic state of the NADPH/NADP(+) system that occur during the transition to Ci-limited conditions remain ill-defined. Analysis of changes in the redox state of cells experiencing Ci limitation reveals systematic changes associated with physiological adjustments and a trend towards the quinone and NADP pools becoming highly reduced. A rapid and persistent increase in F0 was observed in cells reaching the Ci-limited state, as was the induction of photoprotective fluorescence quenching. Systematic changes in the fluorescence induction transients were also observed. As with Chl fluorescence, a transient reduction of the NADPH pool ('M' peak), is assigned to State 2 > State 1 transition associated with increased electron flow to NADP(+). This was followed by a characteristic decline, which was abolished by Ci limitation or inhibition of the Calvin-Benson-Bassham (CBB) cycle and is thus assigned to the activation of the CBB cycle. The results are consistent with the proposed regulation of the @entity3883 and provide new information on the nature of the Chl and NADPH fluorescence induction curves.
