Uptake of heavy metals to the extracellular and intracellular compartments in three species of aquatic bryophyte.

Shoot tips of Fontinalis antipyretica, Scapania undulata, and Fissidens polyphyllus were maintained for 60 min with solutions containing 0, 1, 10, 50, 100, or 200 ppm of Cd, Co, Cu, Ni, Pb, or Zn. A sequential extraction procedure was then used to estimate the amounts of the corresponding metal, and of K and Mg, in the extracellular compartment (extraction with NiCl(2) or EDTA), the intracellular compartment (subsequent extraction with cold dilute HNO(3)), and the particulate fraction (subsequent extraction with hot concentrated HNO(3)). In most cases more metal was taken up to the extracellular compartment than to the intracellular compartment, while particulate-fraction content was negligible. The relationship between metal concentration in the water and metal content in the extracellular compartment was well modeled with a Michaelis-Menten-type equation. Results suggest that in S. undulata extracellular cation-binding sites have a high metal affinity, while in F. polyphyllus it is relatively low. However, postincubation intracellular contents were highest in the latter species. The ranking of the six metals by amounts taken up into the intracellular compartment was the same for all three bryophyte species. Uptake of heavy metals led to considerable losses of intracellular K (probably due to effects on plasma membrane properties), and of extracellular Mg (probably due to displacement from cation-binding sites). Losses of intracellular K were most marked in S. undulata, followed by F. antipyretica. By contrast, S. undulata was the species from which losses of extracellular Mg were lowest.