KINETIC-ANALYSIS OF CD UPTAKE IN CD-TOLERANT AND INTOLERANT POPULATIONS OF THE MOSS RHYTIDIADELPHUS-SQUARROSUS (HEDW) WARNST AND THE LICHENPELTIGERA-MEMBRANACEA (ACH) NYL
Jm. Wells et al., KINETIC-ANALYSIS OF CD UPTAKE IN CD-TOLERANT AND INTOLERANT POPULATIONS OF THE MOSS RHYTIDIADELPHUS-SQUARROSUS (HEDW) WARNST AND THE LICHENPELTIGERA-MEMBRANACEA (ACH) NYL, New phytologist, 129(3), 1995, pp. 477-486
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.