Figure 1.

Model for the role of AtPAM71 in Mn²⁺ homeostasis in chloroplasts. The left part of the scheme shows the wild-type situation where AtPAM71 tentatively functions as Mn²⁺ transporter. Here, sufficient Mn²⁺ is delivered into the thylakoid lumen to ensure optimal oxygen-evolving complex (OEC) formation and hence PSII assembly. The right part of the scheme illustrates the situation in the pam71 mutant. Here, a limited amount of Mn²⁺ import into the thylakoid lumen may occur through the action of Low Affinity Systems (LAS) resulting in decreased oyxgen evolving complex formation. This senario finally results in less photosystem II (PSII) assembly and functionality. PSII subunits are colored in green and light green, the Mn₄CaO₅ cluster (OEC) in pink, the protein environment of the OEC in blue, light blue and gray, transport systems (PAM71 and LSA) in brown and light brown.