The Control of Cadmium Uptake in the Lichen Genus Peltigera

Intra- and extracellular Cd uptake in the lichen genus Peltigerawere investigated, and intracellular uptake found to displayMichaelis-Menten kinetics. Compared with values reported forZn uptake in free-living algae and fungi, Peltigera had lowaffinities for Cd and low maximum uptake rates. Intra-, andto a lesser extent extracellular uptake rates were temperaturedependent. When lichens were incubated concurrently with Cdand equimolar concentrations of a range of other cations, mostwere found to reduce both extra- and intracellular Cd uptake,implying that the Cd uptake systems had low specificities. Mg,though not a strong competitor for extracellular Cd uptake,inhibited intracellular Cd uptake to a similar extent to borderlineelements, and it is postulated that intracellular Cd uptakeoccurs by a system which normally transports Mg. Although concurrently-suppliedcations reduced Cd-induced inhibitions of photosynthesis, thereductions were not proportional to the effect of the cationson intracellular Cd uptake. This indicated that other cationsaffected the toxicity of Cd to photosynthesis by some meansin addition to reducing Cd uptake. Intracellular Cd uptake waslight-stimulated, suggesting that a close relationship existedbetween metal uptake and metabolism. The rate of intracellularCd uptake in the dark was probably not directly linked to thesupply of respirable reserves, as it was unaffected by prolongedstorage in the dark, and was not increased by adding glucose.It is hypothesized that light-stimulated Cd uptake representsactive entry into algal cells, but with uptake in the dark itis not clear which symbiont is involved, and whether energyis required. Key words: Lichen, Cadmium uptake, Temperature, Light, Cation competition