UC San Diego

Toxic heavy metals such as arsenic (As) and cadmium (Cd) contaminate agricultural soils through natural and industrial causes which can lead to hyperaccumulation of toxic metalloids in crops grown on such soils. Phytochelatins, peptides produced by plants in response to heavy metal exposure, have been shown to detoxify toxic heavy metals and arsenic in planta by binding and forming complexes that are then sequestered into vacuoles. This thesis investigates whether Phytochelatin synthase 1 (PCS1) can be overexpressed under a root specific promoter to confine toxic metalloids to underground root systems and prevent hyperaccumulation in aerial and edible tissues of Ozyra Sativa (rice) plants. ICP-MS analysis was used to determine Cd and As content in transgenic and wildtype rice plants. The results showed that root specific overexpression of PCS-1 led to an over 3- fold decrease in shoot accumulation of Cd compared to wild type plants. Additionally, these transgenic plants displayed a root accumulation of Cd that was 6-fold greater per dry weight than wild type roots. Accumulation of As in roots and shoots of transgenic plants followed a similar trend to that of Cd, with roots storing significantly greater amounts of As while shoots stored dramatically less when compared to wild type plants. Altogether, the data suggests that root specific overexpression of PCS1 is effective in redistributing heavy metal accumulation to favor root storage. These findings warrant further research into root specific overexpression of heavy metal tolerance genes to reduce crop accumulation, and thus human consumption of toxic heavy metals.