KINETIC-ANALYSIS OF CD UPTAKE IN CD-TOLERANT AND INTOLERANT POPULATIONS OF THE MOSS RHYTIDIADELPHUS-SQUARROSUS (HEDW) WARNST AND THE LICHENPELTIGERA-MEMBRANACEA (ACH) NYL

Cadmium uptake by photosynthetically Cd-tolerant and intolerant popula tions of the moss Rhytidiadelphus squarrosus (Hedw.) Warnst and the li chen Peltigera membranacea (Ach.) Nyl. was investigated. Intolerant pl ants showed increased intracellular Cd uptake compared to Cd-tolerant material. Kinetic analysis indicated that reduced intracellular Cd upt ake by Cd-tolerant plant material was reflected in an increased K(m) o r decreased V(max) for Cd. Pretreatment with KNO3 modified the extrace llular ion content of plant material, significantly reduced the appare nt K(m) and could increase or decrease the V(max) for intracellular Cd uptake. Changes in kinetic constants caused by K pretreatment could b e related to altered chemical equilibria when plant material was incub ated in Cd solutions. Selective exclusion of Cd from intracellular loc ations was excluded as a tolerance mechanism in R. squarrosus and P. m embranacea. Contrasting kinetic constants for intracellular Cd uptake in intolerant and Cd-tolerant plant material were due to the prevailin g extracellular ion content when collected from the field. In R. squar rosus, K pretreatment resulted in increased uptake capacities and cell -wall binding affinities for Cd in field-grown moss apices. Laboratory -grown apices, following K pretreatment, displayed increased uptake ca pacities but reduced affinities for Cd. Increased extracellular Cd upt ake in K-pretreated moss apices was interpreted as additional weak ele ctrostatic binding. Kinetic analysis indicated that electrostatic bind ing by extracellular sites was less influential than the available sup ply of wall-bounds ions on intracellular Cd uptake by moss apices.