Cationic interactions in caesium uptake by king oyster mushroom (Pleurotus eryngii)

In order to explain influence of common cations (K+, Na+ and Ca2+) on uptake and transport of caesium in macromycetes, a culture of a model mushroom species, king oyster mushroom (Pleurotits etyngii) was set up. Fructification in a growing chamber with stabilised temperature (18 degrees C) and humidity (80%) was preceded by mycelial colonization of the sterilized barley seed medium packed into autoclavable plastic containers. Aliquots of test solutions, containing 0.1 mM caesium chloride carrier traced with (CsCl)-Cs-137 and the selected ions, were dosed into the interphase between the container wall and the spawn block. This allowed to study influence of the added ions on the uptake of caesium in a way unaffected by the used growing medium, e.g. soil, as it was in the previous studies. The experiments demonstrated that the major amount of radiocaesium was biologically bound and accumulated in the fruitbodies to a higher extent (56-69%) than in the mycelium. Addition of 10 mM Na+ decreased the transfer factor for caesium (cap/soil) while addition of Ca2+ caused an increase of this value. The effect of potassium addition depended on its concentration in the solution. Also the Cs/K ratio in caps was significantly influenced by addition of 10 and 100 mM Na+. However, the Cs/K ratio in stipes was affected by Ca2+. Discrimination factors, calculated from specific activities (Cs-137/K-40 cap d.w.)/(Cs-137/K-40 stipe d.w.), were also changed after addition of the studied cations. Since the activities of caesium measured in the fruitbodies of single fungal species strongly depend on the content of co-supplied ions, further proofs should be achieved before using mushrooms as bioindicators of the soil caesium contamination.