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 solution culture system where BaSO(4) precipitation in the growth medium was avoided. This was achieved by alternating every 24 h with a nutrient solution containing Ba (0, 50, 500, or 5000 microM) and all essential elements except S, with another containing S and all other nutrients but no Ba. The external LOEC for acute toxicity symptoms in the form of leaf withering and leaf growth inhibition was 481 microM of free Ba(2+). This was also the LOEC for the complete inhibition of elongation of secondary roots, while for the elongation of the primary root the external LOEC was 4,821 microM. 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 reduced leaf K concentrations was 48 microM free Ba(2+); the corresponding internal LOECs for primary and trifoliolate leaves were 700 and 460 mg kg(-1) DW, respectively.