Figure 8.

Working Model.

Zn deficiency in shoots results in the systemic upregulation of both MTP2 and HMA2 transcript abundance in roots. This leads to enhanced root-to-shoot Zn translocation. HMA2 was previously shown to mediate Zn export from the root symplasm into the apoplastic xylem. In the early differentiation zone of lateral roots, MTP2-mediated transport of Zn²⁺ into the ER allows cell-to-cell movement of Zn through desmotubules into the contiguous ER lumen of the neighboring cell layer via plasmodesmata. This enhances the passage of Zn from the outer epidermal cell layer toward the xylem and consequently to the shoot. Ep, epidermis; C, cortex; En, endodermis; P, pericycle; Xy, xylem.