Fig. 1.

Principle approaches to identify the nature and origin of photosynthetic redox signals. The photosynthetic electron transport chain is depicted schematically. Site-specific inhibitors act at different sites of the chain. Various light regimes can be used to manipulate the electron flow through the chain [PSII-light and high-light conditions lead to preferential or excess excitation of PSII and reduction of plastoquinone (PQH₂); PSI-light leads to presumed excitation of PSI and oxidation of the PQ pool]. Mutations may interrupt or affect the electron flow and generate redox signals (reduction of components before the genetic defect and oxidation after it). Combinations of these approaches can help to define the nature and origin of a redox signal. Negative effects are indicated by bars.