Figure 1.

Schematic diagram of Cd uptake, efflux, vacuolar sequestration and loading into xylem in rice root. Cd is absorbed by root cells from soil, which is mediated by OsNramp1, OsNramp5, OsIRT1, OsIRT2 and OsCd1. After entering root cells, Cd is able to be transported into vacuole by OsHMA3 for sequestration. Cd is also to be chelated with PC or GSH and then transported into vacuole in the form of chelates, but the transporters that can transport PC–Cd and Cd·GS₂ into vacuole have not been identified. OsZIP1, OsHMA9 and OsABCG36 mediate the efflux of Cd, while OsHMA2, OsZIP7 and CAL1 mediate the loading process of Cd into xylem in rice root.