IMMUNOHISTOCHEMICAL LOCALIZATION OF METALLOTHIONEIN IN PLANT-TISSUES

The localization of metallothionein (MT) in the seeds and roots of soybean was investigated by immunohistochemistry. The germinating seeds at 2 hr, 1, 2, 3, 4 and 6 d including 1-mo root tips of soybean (c.v. Toyosuzu) with and without heavy metals (Cu 400-mu-g L-1 or Zn 3-mu-g ml-1) treatment were used to demonstrate the localization of MT by the indirect immunoperoxidase technique using polyclonal rabbit anti-rat MT conjugated to ascaris as a primary antibody. Metallothionein was localized in the proliferating regions such as the embryo in seeds, and root and shoot apices of both the control and heavy metals-treated plants. The intensity of MT staining in the proliferating regions generally increased as the soybean seeds germinate. Starting at about 1 day after germination, MT was found in the veins and vascular bundles suggesting its translocation to other organs. Similar observation hold true in the case of plants treated with heavy metals. This means that heavy metals treatment had no effect on MT localization. However, the heavy metals-treated plants showed higher concentration of MT over the control with respect to the growth stage of soybean seeds. These indicate that MT found in soybean plays a physiological role in heavy metal transport, detoxification and cell division in a similar manner to mammalian MT.