ABSTRACT
The responses of plants to metal exposure have received considerable attention in toxicological and evolutionary contexts. The biochemical and genetic events involved in acclimation responses of plants to metals are less understood. Our intent is to review the responses of plants to metal exposure, propose pathways by which metal “signals” in the environment are transduced to biochemical responses, and to present examples of metal-tolerance mecha nisms based on such pathways. Many metals impact cell physiological function, altering cytoplasmic pH, trans-plasma membrane electrical potential, electrical currents, and ion fluxes. Such alterations are known to affect basic cell activity, including transport functions, cytoplasmic enzyme activity, and gene expres sion, and may activate/induce metal tolerance mechanisms. Exclusion of metals from the cytoplasm may involve changes in the relative proportions of mem brane components, altered transport kinetics of ion uptake systems, or the operation of specific ion transport mechanisms in the plasma membrane and tonoplast that maintain cytoplasmic metal levels below toxic concentrations.
