(137)Cs and (90)Sr uptake by sunflower cultivated under hydroponic conditions. 
The (90)Sr and (137)Cs uptake by the plant Helianthus annuus L. was studied during cultivation in a hydroponic medium.  The accumulation of radioactivity in plants was measured after 2, 4, 8, 16 and 32 days of cultivation.  About 12% of (137)Cs and 20% of (90)Sr accumulated during the experiments.  We did not find any differences between the uptake of radioactive and stable caesium and strontium isotopes.  Radioactivity distribution within the plant was determined by autoradiography. ( 137)Cs was present mainly in nodal segments, leaf veins and young leaves.  High activity of (90)Sr was localized in leaf veins, stem, central root and stomata.  The influence of stable elements or analogues on the transfer behaviour was investigated.  The percentage of non-active caesium and strontium concentration in plants decreased with the increasing initial concentration of Cs or Sr in the medium.  The percentage of (90)Sr activity in plants decreased with increasing initial activity of the nuclide in the medium, but the activity of (137)Cs in plants increased.  The influence of K(+) and NH(4)(+) on the uptake of (137)Cs and the influence of Ca(2+) on the uptake of (90)Sr was tested.  The highest accumulation of (137)Cs (24-27% of the initial activity of (137)Cs) was found in the presence of 10 mM potassium and 12 mM ammonium ions.  Accumulation of about 22% of initial activity of (90)Sr was determined in plants grown on the medium with 8 mM calcium ions.