LAUSR

Abstract Plants of Nicotiana glutinosa L. were semihydroponically cultivated on Hoagland nutrient medium with and without phosphates and supplemented with thorium and tartaric acid; putrescine was sprayed on the leaves. The accumulation of thorium by tobacco and its physiological reactions were monitored. The effect of thorium on the photosynthetic apparatus (contents of photosynthetic pigments and rapid fluorescence of photosystem II (PSII)) was studied. Indicators of abiotic plant stress (e.g., proline, MDA, and antioxidative enzymes), which may also be involved in the detoxification mechanism of plants, were also investigated. The absence of phosphorus from the medium caused an approximately 10-fold increase of thorium accumulation in plants. The amount of thorium in the roots of plants cultivated in phosphate-free medium reached 2.19 and 1.30 mg g−1 of dry matter (DW) with and without putrescine spraying, respectively. However, the selected species—N. glutinosa L.—could not transfer thorium to its upper part at a sufficient level for potential phytoremediation purposes. Application of putrescine on leaves led to increased thorium translocation to shoots, but tartaric acid had no effect. The presence of thorium in plants caused an increase in the content of photosynthetic pigments and a decrease in the values of the selected fluorescence parameters except medium without phosphates. Phosphate-free medium influenced the proline content. The proline concentration reached 80 and 70 μmol g−1 FW in plants with and without putrescine spraying, respectively. These values were up to twice those determined for plants in phosphate medium. The presence of thorium in plants decreased antioxidative enzyme activity (POX, CAT, GST, and APOX) in leaves and increased antioxidative enzyme activity in roots.