Figure 1.

Schematic representation showing the metal species found in the xylem and phloem saps of non-grass (upper panels) and grass plant species (lower panels) grown at low and adequate metal supply (left panels) or at high metal supply (right panels). Metals occurred in free ionic forms and in complexes with different ligands such as nicotianamine (NA), 2′-deoxymugineic acid (DMA), carboxylates (e.g., citrate), histidine (His), phytochelatins (PCs) and proteins. Putative metal species proposed to occur in plant fluids as supported by strong evidence from indirect approaches (e.g., molecular biology and others) are shown with faded symbols. ^*Most of the data with high metal supply have been described in metal hyper-accumulator plant species.