Figure 8.

A working model for Cd allocation mediated by DEF8 in rice. We propose that DEF8 expressed in root pericycle and phloem cells facilitates Cd efflux into apoplast spaces by chelation and secretion, thus loading Cd into xylem for long distance transport from root to aerial parts, where Cd is further loaded into phloem, possibly via LCT1, HMA2, or other unidentified transporters. Grain Cd efflux from phloem to apoplast is facilitated by DEF8 via a similar mechanism in roots. The apoplast Cd possibly moves and accumulates in the endosperm via free diffusion or active transport across the membrane of the pigment strand cells surrounding the endosperm. The blue line in the grain indicates vascular bundles of brown rice. DEF8-Cd represents the complex which is not actually detected but by prospection from experimental evidence, meanwhile free DEF8 exists in the apoplast prior to Cd treatment.