Table III.
Results of fitting the XAS spectra (energy region of the EXAFS analysis, i.e. 20 to 500 eV above the edge) with a linear combination of the measured data sets of representative model compounds
The graphs of the fits for young leaves are shown in Figures 2 and 3. Those of all other samples are displayed in the figures of the supplemental material. se, Mathematical ses of fit (one sigma level). The error of the method as such is higher due to systematic errors; also, the variability of the plants has to be kept in mind. Both contribute to the differences between samples of the same type, as shown for the Cd edge of young and mature leaves, 100 μm Cd + 10 μm Zn. –, Not measured.
| Sample | Cd ligands (±se; Cd edge measurement) | Zn ligands (±se; Zn edge measurement) |
|---|---|---|
| Young leaves, 100 μm Cd + 10 μm Zn | 20% (±3%) His | 20% (±3%) His |
| 46% (±3%) O ligandsa | 80% (±2%) O ligandsa | |
| 35% (±1%) S ligandsb | ||
| See above, second sample | 10% (±5%) His | - |
| 56% (±4%) O ligandsa | ||
| 34% (±1%) S ligandsb | ||
| Mature leaves, 100 μm Cd + 10 μm Zn | 28% (±3%) His | 1% (±3%) His |
| 38% (±2%) O ligandsa | 99% (±2) O ligandsa | |
| 34% (±1%) S ligandsb | ||
| See above, second sample | 26% (±6%) His | - |
| 54% (±5%) O ligandsa | ||
| 21% (±2%) S ligandsb | ||
| Mature leaves, 50 μm Cd + 10 μm Zn | 13% (±6%) His | - |
| 63% (±5%) O ligandsa | ||
| 24% (±2%) S ligandsb | ||
| Mature leaves, 0 μm Cd + 10 μm Zn | - | 40% (±5%) His |
| 60% (±3%) O ligandsa | ||
| Senescent leaves, 100 μm Cd + 10 μm Zn | 25% (±5%) His | - |
| 59% (±5%) O ligandsa | ||
| 16% (±2%) S ligandsb | ||
| Dead leaves, 100 μm Cd + 10 μm Zn | 39% (±3%) His | 70% (±3%) His |
| 30% (±3%) O ligandsa | 30% (±2%) O ligandsa | |
| 31% (±1%) S ligandsb | ||
| Mature petioles, 100 μm Cd + 10 μm Zn | 0% (±6%) His | 34% (±5%) His |
| 75% (±5%) O ligandsa | 66% (±3%) O ligandsa | |
| 25% (±2%) S ligandsb | ||
| Senescent petioles, 100 μm Cd + 10 μm Zn | 11% (±5%) His | - |
| 70% (±5%) O ligandsa | ||
| 20% (±2%) S ligandsb | ||
| Mature stems, 100 μm Cd + 10 μm Zn | 27% (±3%) His | 38% (±4%) His |
| 36% (±2%) O ligandsa | 62% (±3%) O ligandsa | |
| 37% (±1%) S ligandsb | ||
| Mature stems, 0 μm Cd + 10 μm Zn | - | 46% (±6%) His |
| Senescent stems, 0 μm Cd + 10 μm Zn | 3% (±4%) His | - |
| 68% (±4%) O ligandsa | ||
| 29% (±1%) S ligandsb |
No significant difference between the EXAFS spectra of organic acid and aqueous complexes were found; therefore, an average of both data sets was used as model for fitting. b The Cd-glutathione complex was used as model.