Figure 10.

Working Hypothesis on the Function of the Flv2/Flv4 Heterodimer and the Sll0218 Protein during Photosynthesis at Low Ci (Air Level of CO₂) Conditions.

(A) In darkness, the Flv2/Flv4 heterodimer is mostly in soluble form in the cytoplasm. However, transient binding of the Flv2/Flv4 heterodimer to the thylakoid membrane (TM) is postulated to occur upon increase in Mg²⁺ concentration on the cytoplasmic surface of the thylakoid membrane when the lights are turned on. This creates an alternative electron transfer route from PSII to the Flv2/Flv4 heterodimer that is made possible by Sll0218-induced subtle changes in PSII.

(B) Hypothetical model for the involvement of the Flv2/Flv4 and Sll0218 proteins in energy transfer from PBS to PSII and electron transfer from PSII to the Flv2/Flv4 heterodimer at low Ci. Mg²⁺-induced attachment of the Flv2/Flv4 heterodimer to the thylakoid membrane coordinates both the energy transfer from PBS to PSII and the electron transfer from PSII to the Flv2/Flv4 heterodimer in PSII centers slightly modified by the Sll0218 protein upon the assembly process. WT, the wild type.

(C) Scheme of electron transport processes in the presence of the Flv2/Flv4 heterodimer and the functional mode of the artificial electron acceptors of PSII, DCBQ, and DMBQ.