| Plants depend on their roots to gather nutrients for their growth and survival. However, the efficacy with which roots compete for nutrients in the exposure media, relative to other solution ligands, has not been clearly resolved. As a result, the free ion activity model (FIAM), can-ently used to predict plantmetal binding, does not include the influence of the root on metal speciation chemistry and subsequent metal uptake. Defining the root as a competitive ligand would transform the FIAM into a biotic ligand model (BLM), making it more comprehensive in scope so that it may, in part, overcome the limitations to predicting metal bioavailability in chemically diverse exposure media.; The current thesis is aimed at laying the groundwork for a BLM for Cu binding to durum wheat (Triticum turgidum L. var durum, cv 'Arcola'). Conditional stability constants (log K Root-Me) and binding site densities (XRoot-Cu) for root-Cu binding were determined, and the effect of exposure duration, transpiration, plant maturity, exposure intensity, the use of metal buffers, and different endpoints (i.e., toxicity vs. accumulation), on their magnitude was investigated.; The results demonstrate that roots have both low- and high-affinity metal ligands in the apoplasm, and that the high-affinity ligands, such as proteins, play a very important role in selective metal acquisition.; The magnitude of log KRoot-Cu values was less sensitive to variations in exposure duration, transpiration, and plant maturity than values for XRoot-Cu, and were also relatively constant when the system under study was not in chemical equilibrium. Also, the use of a metal buffer, NTA, was found to be critical in deriving log KRoot-Cu values for low metal exposures, likely due to its ability to overcome diffusion and supply limitations to root-metal binding. These results are important because the BLM will eventually be applied to soils, where the root environment is rich in ligands which will also have a profound influence on exposure solution chemistry and root-metal binding. |
