| Environmental pollution is a continuing global problem. Among various pollutants, toxic heavy metals contribute to a great proportion of soil and water pollution and causes major problems to human beings, animals as well as to plants. It is becoming a critical concern and needs rapid and effective remediation. The conventional remediation methods are no longer economically valid and practical for environmental cleanup, therefore, they have to be replaced with an advanced and modern technology and that is: "using plants", which is referred to as "phytoremediation".;This study is focused on arsenic (As) and lead (Pb) pollution and the prospect of remediation by using certain plants that are capable of accumulating extraordinary high amounts of toxic heavy metals. This is referred as to "heavy metal hyperaccumulation". Unfortunately the biochemical and physiological mechanisms responsible for this phenomenon are still not completely understood. Therefore, investigation on the involvement of the plant's proteome in metal accumulation, stress, and tolerance offers a new platform to understand the responsible biochemical and physiological mechanisms. This is the foundation of this dissertation.;The Dwarf Sunflower, Helianthus annuus, was used to study the proteomic responses of the plants to exposure to As and Pb. Differential expression of several proteins was shown by the use of one- and two-dimensional gel electrophoresis coupled with tandem mass spectrometry. Polyethelene glycol fractionation was used as the most suitable protein extraction method for Sunflowers. The enzyme chitinase was one of the first proteins identified that show a reproducible up-regulation in response to both As and Pb. This protein is involved in a general defense mechanisms to stress conditions. Other proteins that were over-expressed were thaumatin, heat shock protein, ATP synthase alpha and beta subunits, malate dehydrogenase, carbonic anhydrase, RuBisCO activase, triose phosphate isomerase and nitrophenyl phosphatase. All these have vital roles in a metabolic response to metal stress.;A model organism, Chlamydomonas reinhardtii, was chosen to study at the cellular level the molecular mechanism of response to As exposure. Proteins, over-expressed and induced by As stress, were associated with the removal of damaged proteins, oxidative stress, increased energy demand, protein synthesis and protein folding. The majority of the cell's reaction appears mainly to be a response to protein and oxidative damage which is only slightly different from what was observed for Sunflowers.;Finally a known arsenic hyperaccumulator, the Fern Pteris vittata, was used to see if it showed a similar response to arsenate. It also was tested if the amount of arsenate makes a difference in the Ferns' response at the protein level. Forty (40) proteins were differentially expressed in response to arsenic exposure and the identified proteins reveal that arsenic predominately affects proteins belonging to photosynthesis, carbon metabolism, protein turn-over and some proteins that are generally recognized as stress-related. Thus, even the hyperaccumulating Fern deals with arsenic toxicity by up-regulation of metabolic pathways and general damage repair pathways. |
