FIGURE 1.

Simplified representation of the main energy pathways in and around PSI and PSII, down to ferredoxin (Fd) and downstream. Some of the JIP-test parameters were indicated. Since most ChlF originates in PSII antenna, J₀^ABS represents the rate of photon absorption by all PSII antenna pigments. The dissipated energy flux J₀^DI represents the part of the absorbed photon flux dissipated through direct fluorescence and other non-radiative processes (as heat), and the trapped exciton flux J₀^TR represents the rate of exciton trapping by the PSII RC P₆₈₀. The trapped energy is used for charge separation using the components of the PSII RC, i.e., pheophytin molecules (Phe) and Q_A and Q_B quinones [linked to D1 and D2 proteins not represented, Q_A (bound to D2) and Q_B (bound to D1)]. The complex Mn₄O₅Ca|Y₂ corresponds to the oxygen-evolving complex. The flux J₀^ET2 represents the electron transport flux from Q_A to Q_B. J₀^RE1 represents the rate of electrons from Q_B to PSI acceptors. J_C, J_O, and J_A represent the electron flows for carboxylation, oxygenation, and alternative sinks, respectively. PQ and PC represent plastoquinons and plastocyanins. Violet arrows are associated to the JIP-test. Blue arrows correspond to the fluxes evaluated from combined measurements of modulated ChlF and gas exchanges (Valentini et al., 1995). The orange arrow corresponds to the CEF (Kotakis et al., 2006) and the red to the chlororespiration (Rumeau et al., 2007).