UC San Diego

The industrial and urban evolution of the modern world has contributed to the innovative developments and economic growth of many countries. This growth has also resulted in elevated levels of heavy metal pollutants in the biological systems of these nations, such as their cropland and bodies of water. This becomes a predicament, as some of these nations are leading producers of agricultural products worldwide. Since the exposure of heavy metal toxicants via ingestion of contaminated crops can cause many serious illnesses to humans, this dilemma has received global attention from health organizations and science communities. To contribute to these efforts, this thesis research project aims to evaluate a heavy metal phytoremediation technique in rice plants known as “phytostabilization”. Phytostabilization refers to the immobilization of heavy metal pollutants in the roots of plants to prevent their uptake into the shoots, leaves, and seeds. This was tested with transgenic rice lines with root-targeted overexpression of the following transgenes: Phytochelatin Synthase Gene from T. aestivum (TaPCS1) and Heavy Metals Associate3 gene from A. thaliana (AtHMA3). TaPCS1 overexpressing rice lines were exposed to different concentrations of both cadmium (CdCl2) and arsenite (As(III)), while AtHMA3 overexpressing lines were only exposed to different concentrations of cadmium (CdCl2). ICP-MS analysis was utilized to measure heavy metal contents in the root vs. shoot tissues of the aforementioned rice lines upon exposure to their respective heavy metal conditions. The preliminary results of this study suggested that rice lines with root-targeted overexpression of AtHMA3 were able to achieve lower Cd accumulation in the shoot tissues when compared to the wildtype controls. Furthermore, there was promising evidence that rice lines with root-targeted overexpression of TaPCS1 exhibited lower Cd and As(III) accumulation in the shoot tissues than the wildtype controls; however, further experimentation must be done on multiple independent transgenic lines and several exposure regimens.