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244 P. Kotrba

Fig. 12.1 Molecular determinants and mechanisms involved in metal–plant interaction. The
metal is mobilized in the rhizosphere by secreted acidic or chelating molecules of both plant
(root exudates) and microbial origin. The soil microflora may also trigger formation of organic or
inorganic secondary minerals (carbonates, phosphates and hydroxides increases, oxalates), ren-
dering the metal less available to plant. Endophytic bacteria inhabiting the plant mainly contribute
mainly by promoting plant growth (support, e.g., the acquisition of micronutrients or the produc-
tion of plant hormones). Root-to-shoot translocation of metals, either as hydrated ions or
metal–ligand complexes, occurs via the xylem. Metals reaching the aboveground apoplast are
than differentially captured in different cell types, moving also cell-to-cell through plasmodesmata
(not shown). Transporters and transporter families involved in uptake and redistribution of metals
within plant body and cells are indicated: ZIP zinc-regulated, iron-regulated transporter protein
family; COPT copper transporter family (syn. CTR); HMA heavy metal ATPase of P 1B -type