FACTORS AFFECTING THE KINETICS OF INTRA-AND EXTRACELLULAR CADMIUM UPTAKE BY THE MOSS RHYTIDIADELPHUS SQUARROSUS.

The responses of field-grown and cultured shoots of a moss, Rhytidiadelphus squarrosus (Hedw.) Warnst, to Cd were investigated. Respiration was not affected, but photosynthesis was progressively reduced with increasing Cd uptake. Field-grown shoots of two morphologically distinct populations differed in their photosynthetic responses to Cd. This could be related to different rates of Cd uptake by the two populations. During storage of Cd-treated shoots, movement of extracellular Cd to an intracellular location occurred, and this was reflected in altered photosynthetic rates. The maximum extracellular uptake capacity and affinity for Cd were identical for the two populations of field-grown shoots. Field-grown material from the two populations differed significantly in their intracellular Cd uptake characteristics, cation contents, gas exchange rates and dry weights per unit length. These differences were eliminated by laboratory culture. Cultured shoots had increased affinity for both intra- and extracellular cadmium uptake compared to field-grown shoots. The results indicate that the activity of Cd and other divalent cations at the plasmalemma may control the affinity for and accumulation of Cd by this moss. The results are discussed in terms of the design of experiments in studies of ion uptake and tolerance in bryophytes.