Abstract
The mechanism by which plants regulate channeling of photosynthetically derived electrons into different areas of chloroplast metabolism remains obscure. Possible fates of such electrons include carbon assimilation, nitrogen assimilation and signaling pathways, or return to the plastoquinone pool through cyclic electron flow. In higher plants, these electrons are made accessible to stromal enzymes, or for cyclic electron flow, as reduced ferredoxin (Fd), or NADPH. We investigated how knock-out of an Arabidopsis ferredoxin:NADPH reductase (FNR) isoprotein, and the loss of strong thylakoid binding by the remaining FNR in this mutant, affected channeling of photosynthetic electrons into NADPH and Fd dependent metabolism. We found significant differences in electron channeling in the chloroplasts of mutant and wild type plants, and in addition uncovered evidence that FNR may be involved in stress signaling. Taken together, our results demonstrate the integral role played by FNR isoform and location in the partitioning of photosynthetic reducing power.
