Figure 1.

Transport proteins for Ca²⁺ and Mn²⁺ discussed in this review. Pumps (triangles), transporters (ellipses), and channels (rectangles) that were experimentally shown to permeate Ca²⁺ (blue), Mn²⁺ (magenta), or both (blue/magenta) are displayed in a hypothetical plant cell containing the organelles discussed in this review. Only Arabidopsis proteins are shown, except for LjCASTOR and MtCNGC15s, for which a function of the Arabidopsis homologs as Ca²⁺ channels has not been examined yet. Characterized orthologs of Arabidopsis proteins described in the text are listed in Table 1. Note that the absence of an experimentally confirmed substrate, for example, Mn²⁺ in the case of Ca²⁺ channels (GLR, CNGC, and TPC1) does not exclude its permeation. Conductance of Mn²⁺ by (c)MCUs is inferred from their mammalian homologs. The permeation of Ca²⁺ by NRAMPs can be excluded on a structural basis, as discussed in the text. ER, endoplasmic reticulum; NE, nuclear envelope; PVC, pre-vacuolar compartment; TGN, trans-Golgi network.