DIFFERENT CHARACTERISTICS OF ROOTS IN THE CADMIUM-TOLERANCE AND CD-BINDING COMPLEX-FORMATION BETWEEN MONOCOTYLEDONOUS AND DICOTYLEDONOUS PLANTS

Effects of Cd2+ on growth and Cd-binding complex formation in roots were examined with various seedlings of mono- and dicotyledonous plants. Maize, oat, barley and rice exhibited the greater tolerance to Cd2+ (100 muM) than did azuki bean, cucumber, lettuce, pea, radish, sesame and tomato (10-30 muM). Azuki bean was the most sensitive of Cd2+ (<10 muM). Under these Cd-treatments, cereal roots accumulated Cd2+ in the cytoplasmic fractions and transported Cd2+ into the same fractions of shoot tissues, to larger extents than did dicotyledonous roots. Cereal roots synthesized a Cd-binding complex containing phytochelatins in the cytoplasmic fractions, depending upon Cd2+ concentrations applied (30-100 muM). Such a complex was not detected from the same fractions of dicotyledonous roots treated with Cd2+. These results suggest that the Cd-binding complex formation has an important role in the tolerance of cereal roots against Cd2+.