Genotypic Influence on Metal Ion Mobilization and Sequestration via Metal Ion Ligand Production by Wheat

Intracellular production and root exudation of metal ion Iigands (MIL) are keys to metal ion mobilization and sequestration by vascular plants. This is well-exemplified by the exudation of phytosiderophores such as mugineic acid and derivatives in the acquisition of Fe (III) and Zn (II) by graminaceous plants. However, the genetic and biochemical mechanism(s) for the mobilization and sequestration of most pollutant metal ions remain unknown, due largely to a lack of knowledge in MIL involved in the process. This information is critically needed for developing and engineering plant-based remediation of metal contamination at DOE, DOD, and other industrial facilities. Here, we investigated the influence of elevated metal (Zn, Cu, Ni, Mn, and Cd) ion treatment on root ixudation, tissue MIL profiles, and metal accumulation in Chinese spring (CS) wheat, its 7 genotypes prepared from disomic addition of the wheatgrass chromosomes to CS, and the amphiploid between the two species. Broad-screen and structure elucidating nuclear magnetic resonance spectroscopy and gas chromatography-mass spectrometry were employed to obtain comprehensive profiles of MIL in root exudates and tissues, difficult to achieve with conventional approaches. In addition, thiol-rich peptide profiles were acquired using fluorescent bromobimane tagging and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, while comprehensive metal ion profiles were obtained using X-ray fluorescence. Genotypic covariation was noted between metal ions (Mn, Fe, Cu, and Zn) and such MIL as 2′-deoxymugineic acid and acetate in root exudates and citrate and malate in roots. Profiles of phytochelatin-like peptides also displayed genotypic variations and strong correlation with Cd accumulation. These results suggest possible chromosomal location(s) of gene(s) governing metal ion mobilization and sequestration in wheat.