Barriers and Carriers for Transition Metal Homeostasis in Plants

Transition metals are a type of metal with high chemical activity and play critical roles in plant growth and development, reproduction and environmental adaptation, as well as for human health. However, the acquisition, transportation and storage of these metals always pose specific challenges due to their nature of high reactivity and poor solubility. In addition, distinct yet interconnected apoplastic and symplastic diffusion barriers impede their movement throughout the plants. Plants have evolved sophisticated carrier systems to facilitate their transport, which relies on tight coordination of vesicles, enzymes, metallochaperones, low-molecular weight metal ligands, and membrane transporters for metals, ligands and metal-ligand complexes. Here we review recent advances in transition metal homeostasis in plants, focusing on barriers to transition metal transport and carriers that facilitate their passage through these barriers.