Assessment of barium toxicity in bush beans

External and internal lowest observed effect concentrations (LOECs) for Ba in bean plants (Phaseolus vulgaris) were established using a nutrient solut ion culture system where BaSO4 precipitation in the growth medium was avoid ed. This was achieved by alternating every 24 h with a nutrient solution co ntaining Ba (0, 50, 500, or 5000 muM) and all essential elements except S, with another containing S and all other nutrients but no Ba. The external L OEC for acute toxicity symptoms in the form of leaf withering and leaf grow th inhibition was 481 muM Of free Ba2+. This was also the LOEC for the comp lete inhibition of elongation of secondary roots, while for the elongation of the primary root the external LOEC was 4,821 muM. Barium interfered with both the sulfate transport from roots to shoots and the import of Ca into leaves. However, K was the most Ba-sensitive nutrient. External LOEC for re duced leaf K concentrations was 48 muM free Ba2+; the corresponding interna l LOECs for primary and trifoliolate leaves were 700 and 460 mg kg(-1) DW, respectively.