CATIONIC INTERACTIONS IN RADIOCESIUM UPTAKE FROM SOLUTION BY SPINACH

Interionic effects on radiocaesium uptake in spinach (Spinacia olerace a L, cv. Subito) were measured in a solution culture experiment. In to tal, 15 different nutrient solutions, spiked with Cs-137, were prepare d in which K, NH4, Ca and Mg concentrations were varied at four differ ent total salt concentrations between 5.3 meq l(-1) and 21.2 meq l(-1) . The range of cationic concentrations studied was: K, 0.53 to 10.4 mm ol l(-1); NH4, 0 to 8.47 mmol l(-1) Ca, 0.15 to 5.0 mmol l(-1), Mg, 0. 08 to 2.0 mmol l(-1). The plant/solution Cs-137 transfer factor (TF) v aried between 41 l kg(-1) and 117 l kg(-1). Radiocaesium levels in the plants were poorly, but positively, correlated with the K concentrati on in solution. However, radiocaesium levels were significantly reduce d by increasing Ca + Mg concentrations in solution. Between 10.06 and 1.06 mmol l(-1) K, radiocaesium levels in 20-day-old plants were only slightly affected if K was replaced by NH4 at almost constant Ca + Mg concentrations. The negative effect of Ca + Mg concentrations on Cs-13 7 uptake is interpreted from their effect on Cs-137 loading in the apo plast of the root cortex. A quantitative relationship is presented bet ween the Cs-137 TF and the fractional loading of Cs-137 in the apoplas t, which is calculated by ion exchange laws, This relationship is line ar (R(2) = 0.81) for the 15 different solutions studied. Copyright (C) 1996 Elsevier Science Limited