These x-ray "maps" generated at NSLS-II show the distributions of iron (top row) and copper (bottom row) throughout mature leaf petioles, both in unaltered plants (left, WT) and mutant plants (right, opt3). Warm colors (red, orange, and yellow) indicate high concentrations, and cool colors (green and blue) indicate low concentrations. Xy points to the xylem, Ph points to the phloem, and FC points to the fascicular cambium, another type of plant tissue. The maps showed that the mutant plants exhibited larger concentrations of iron in the xylem and, surprisingly, that the copper distribution resembled the iron distribution.