Distribution patterns of the metal pollutants Cd and Ni in soybean seeds

Soybean (Glycine max) plants were grown to maturity in nutrient solution, amended with either Cd or Ni. The distribution of these metals in mature seeds was examined with micro-PIXE. The levels of Cd were too low for mapping and only average concentrations from selected regions could be obtained. Cd was localised mainly in the seed coat and cotyledons, with very little in the embryo axis. Levels of Ni were high enough to obtain the distribution maps. This metal was mainly concentrated in the axis, particularly in the apical meristem and cortex, and least in the cotyledons. Localisation of Ni within different tissues of the embryo was facilitated by mapping of Ca which is present in the cell walls of plants. This enabled the different plant tissues of the seed embryo to be identified. Micro-PIXE is a valuable tool for localising the distribution of metal pollutants in plant tissue.