Research Interests:
My research interests involve achieving a greater understanding of plant-metal interactions. Metals are critical factors in the normal functioning of plants but some can represent hazards to plants as well as to consumers of plants. My work has focused largely on the physiological processes underlying movement and retention of the potentially toxic heavy metal cadmium in durum wheat plants. Durum wheat has a tendency to accumulate cadmium in grain when it is grown in soils which contain cadmium as a trace component. My research has revealed insights into factors that affect cadmium entry into and movement within the plant body. By using synthetic chelating agents to control free metal activities at levels similar to those found in field soil solutions, I have characterized the uptake kinetics of both cadmium and the chemically similar (and nutritionally essential) zinc. These metals are taken up into root cells via a saturable concentration-dependent process that is probably mediated by a membrane-localized transport system. My work has shown that zinc can compete with cadmium for entry into root cells and can also affect fluxes of cadmium within the plant through phloem tissue. An important step in controlling the amount of cadmium that accumulates in wheat grain is to inhibit movement of cadmium out of roots and into shoots. I have produced evidence that contradicts a hypothesis that root-to-shoot movement of cadmium is controlled by sequestration in root cell vacuoles as a complex with phytochelatins. Rather, upward translocation is likely related to the loading of cadmium from root cells into the xylem, which constitutes the major pathway of solute movement from roots to shoots.
Essential metals such as zinc and iron are important plant nutrients, acting as components of enzymes and other cellular constituents. An important goal of plant nutrition research is to understand the basis by which plants acquire and utilize mineral nutrients. Studying the pathways of zinc and cadmium uptake and distribution has led to insights into similar processes for other metal micronutrients such as iron and manganese. I have recently joined an effort to increase our understanding of the bioavailability of iron in maize plants and in human consumers of maize grain. Research has shown that there is a large amount of genetic variation among maize varieties in their ability to store iron in grains. Although increasing the iron concentration in maize grain would appear to be a good approach to improving iron nutrition in consumers of maize, studies have shown that there is no consistent correlation between grain iron concentration and iron uptake into human intestinal cells. The use of an in vitro intestinal cell culture system has shown that bioavailability of iron is not necessarily linked to iron concentration per se. It appears that some intrinsic factor(s) in maize grain may have an effect on suppression or enhancement of iron absorption. Identifying this factor(s) is an important goal of my future research efforts.
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