Root elongation of Norway spruce (Picea abies (L.) Karst.) seedlings was inhibited in the presence of 5 microM Cd, but was unaffected by a Cd concentration at 0.05 microM. Nutrient solutions labeled with (109)Cd were used to investigate the influence of pH, cations and the metabolic inhibitor 2,4-dinitrophenol (DNP) on the uptake of Cd by roots of intact spruce seedlings. Extracellular Cd was removed by washing the roots, and the relative amounts of Cd in the root apoplast and symplast estimated. In the presence of DNP, Cd uptake was reduced at 0.05 microM (non-toxic) but not at 5 microM Cd (toxic). At 0.05 microM Cd, the uptake of Cd into both the apoplast and symplast was dependent on the pH of the nutrient solution. Lower pH decreased Cd accumulation. Aluminum supplied at 100 or 500 microM lowered the Cd concentrations of both the apoplast and symplast. An increase in Ca or Mg supply reduced the Cd concentration of the apoplast but not of the symplast. In the presence of 5 microM Mn, the concentration of Cd in the symplast decreased by 44% compared to the control (1 microM Mn). High concentrations of Zn or Hg did not affect the Cd concentration of the roots.