Heavy Metal Uptake in Plants

Our laboratory is very interested in understanding heavy metal uptake and translocation in plants. We are studying cadmium because it is an important toxin in humans, especially in industrialized countries. Plants have been shown to be the primary source of the metal in human diets. Cadmium occurs naturally in the soils of the Great Plains and is found in many other agricultural soils due to contamination from mining, manufacturing, and use of some fertilizers. Cadmium is a problem because many plants (e.g., sunflowers, tobacco) actively accumulate the metal.

Cadmium is sequestered in plants in complexes with a small peptide (phytochelatin) and sulfide. What happens to the metal after the formation of these complexes is not understood, and little is known about remobilization within and between tissues. Paul Hoffer's work is beginning to address these questions by examining the accumulation of cadmium in the leaves and roots of oats grown hydroponically in cadmium-containing media. Paul has monitored the movement of the metal from roots to leaves and into the developing fruit. His data show that the metal stored in the leaves is remobilized and transported to developing fruits. Using aphids to tap the phloem, Paul has also shown that the metal is moving in this conductive tissue with the carbohydrates and other nutrients that are needed for normal seed development.

Paul is currently working to help identify the form in which the cadmium is translocated within the phloem. His work in conjunction with studies on the transporters involved in cadmium uptake and remobilization may someday help to provide the means of developing plants that do not store cadmium in the tissues utilized by people.