| Glutathione (GSH) has long been known to be an essential molecule in a number of important basic cellular functions including detoxification of reactive oxygen species, transport and storage of organic sulfur, and regulation of the cell cycle. Furthermore, GSH is essential in the detoxification of some heavy metals including cadmium through the production of phytochelatins. Because the accounts of heavy metal pollution are increasing due to human activities, heavy metal toxicity in plants is an important topic of study. To investigate the role of GSH-related functions in response to cadmium exposure I examined three distinct levels of GSH involvement in overcoming cadmium toxicity in the model plant, Arabidopsis thaliana.; First, the expression of Arabidopsis phytochelatin synthase ( AtPCS1) was targeted to the green portions of the plant in hopes of establishing plants capable of accumulating more cadmium in leaves. Transgenic lines were more tolerant of cadmium and had increased phytochelatin synthase mRNA accumulation and in vitro enzyme activity than their genetic parent. Despite this, transgenic lines did not produce more phytochelatins in planta, and the leaf-to-root distribution of cadmium accumulation did not change. While the initial goal of this project was not realized, this study led to a greater understanding of control mechanisms preventing cadmium accumulation.; Second, utilizing wildtype (WT) and two mutants, vtcl-1 and cad1-3, the response of components of the ascorbate-Guathione cycle to cadmium stress was investigated. These three lines responded similarly to changes in antioxidant enzyme activities, but had differing transcript levels of biosynthetic genes, anthocyanins, and antioxidants. It was found that the vtc1-1 mutant has higher GSH levels than WT and is capable of producing higher concentrations of phytochelatins.; And third, how the proposed glutathione degradation pathway in Arabidopsis is affected by cadmium exposure was studied. Evidence is given that the gamma-glutamyl transpeptidase system in Arabidopsis is activated by the presence of cadmium. Implications of this finding are discussed.; These three distinct projects have led to a greater understanding of the glutathione response to cadmium as well as insight into the various controls of this system. |
