Uptake of Cadmium and its effect on the physiology of the liverwort Dumortiera hirsuta (SW) Nees and the moss Atrichum androgynum (CM) Jaeg.
Mautsoe, Puseletso Jacinta.
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In this thesis, the uptake kinetics of Cd by the liverwort D. hirsuta and the moss A. androgynum were investigated. In preliminary experiments, the toxicity of Cd to the bryophytes was investigated by characterising the effects of Cd on photosynthesis and K loss. Experiments were carried out to explain the existence of variation between different collections observed in uptake kinetics in the liverwort D. hirsuta. Photosynthesis in D. hirsuta was more sensitive to Cd than photosynthesis in A. androgynum. The sensitivity was directly related to intracellular Cd concentrations. D. hirsuta accumulated considerably higher concentration of intracellular Cd than A. androgynum. Cd caused intracellular K loss in D. hirsuta but not in A. androgynum. Extracellular Cd uptake was rapid and independent of metabolism. Intracellular Cd uptake as a function of Cd concentrations followed Michael is-Menten kinetics. Intracellular Cd uptake in D. hirsuta was affected by age of the plant, K pretreatment and the site where plants were collected. The moss A. androgynum displayed Cd uptake acclimation when uptake was measured at low temperatures. The results indicated that uptake kinetics could be affected by seasonal variation. Tolerance of Cd in the moss A. androgynum could be induced by pretreating the plants with low concentrations. The moss possibly excludes Cd from the cytoplasm and thus reduces the concentration of Cd in the cytoplasm to below toxic level.