Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Biology

Collaborative Specialization

Environment and Sustainability

Supervisor

Macfie, Sheila M

Abstract

With cadmium uptake by plants posing a risk to plants and consumers alike, strategies to reduce metal uptake are desirable. One strategy may be to apply selenium (as selenate) to the growth medium. I hypothesized selenate would yield greater lignification, with a higher proportion of cadmium bound to root cell walls. Consequently, higher selenium in plants would result in greater tolerance to cadmium. Additionally, since selenate is taken up in place of sulphate, providing the plants with high sulphate would inhibit uptake and translocation of selenium, mitigating selenate’s benefits of reducing cadmium uptake and translocation. Experimental results did not support these hypotheses. Selenate did not affect lignification, nor yield lower cadmium uptake and translocation. Rather, shoot selenium and cadmium concentrations were positively correlated. Thus, the safety of consuming plants from where cadmium concentrations are elevated appears unlikely to be improved by applying selenate, and potential for harm may increase.

Summary for Lay Audience

Polluted soils are sometimes used for agriculture. While problematic and inadvisable, with land scarcity, alternatives may not be feasible. One contaminant of concern is the toxic metal cadmium. Plants grown on cadmium-contaminated soils can pose a health risk to consumers. Another issue pertaining to the food supply is deficiency in selenium, an essential micronutrient for animals. This deficiency is estimated to affect 500 million to 1 billion people worldwide. When selenium is applied to plant cells, it results in structural and chemical changes. Specifically, an increase in lignin concentrations has been reported. Lignin is a molecule that helps to give strength to plant cells. Increased lignin associated with selenium treatments has been reported to reduce the amount of cadmium that enters the cell. Thus, applying selenium in the presence of cadmium was expected to have two benefits. Firstly, the plant was expected to take up less cadmium. Secondly, the plant would have a higher selenium content, providing more of this essential micronutrient to the consumer. Whether this strategy would work was tested in 8 plant species, including 5 that are common agricultural crops or vegetables, all grown hydroponically. Since the amount of another nutrient, sulphate, was expected to impact how much selenium the plant took up, plants were grown in treatments with high sulphate and sufficient sulphate. The amount of lignin in the roots was measured in 3 of the species to test the effect of selenium on the plants. Then, for all 8 species, concentrations of cadmium and selenium in the aboveground portions of the plants were measured. Contrary to expectations, selenium did not result in higher lignin concentrations in the plants’ roots, nor did it reduce the amount of cadmium taken up. Rather, the more selenium the plants took up, the more cadmium they tended to take up. Given that lignin concentrations did not increase with selenium, the lack of effect on cadmium was unsurprising, albeit disappointing. These results indicate applying selenium to crops grown in soils with elevated levels of cadmium may increase the risk of harm, rather than providing a benefit.

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