GC-MS Analysis of Se-Volatiles and Se-Amino Acids in Brassica juncea and Populus tremula x alba Grown in Selenium-Laden Soils

Adam Rudolph, Norwich University, Northfield, VT

Advisor: Dr. Alison J. Fisher

Adam presented his research at the Annual Meeting of the Vermont Genetics Network

at the University of Vermont on August 18, 2002.

Abstract

Selenium (Se) pollution in soil and groundwater poses a serious threat to animals and humans. Se-resistant plants that naturally take-up, accumulate, and volatilize Se are currently being used to clean-up Se-contaminated sites in the environment. Most plant species being used to remove Se from soil and water are herbaceous (i.e., Brassica species) and are limited by shallow root systems. Recently, however, hybrid poplar (Populus tremula x alba) trees were shown to accumulate and volatilize Se from hydroponic solution, making hybrid poplar a promising candidate for the removal of environmental Se in the future. It is not known whether hybrid poplar utilizes similar biochemical mechanisms for Se-accumulation and volatilization as known Se-resistant plant species (Figure 1, Figure 2). Therefore, we wished to analyze and compare both Se-volatiles and stored Se-amino acids from Indian mustard (Brassica juncea) and hybrid poplar. To this end, we developed methods to trap and analyze volatile species released from plants grown in Se-laden soil. We constructed trapping chambers (Figure 3) in which volatiles from 12 plants can be collected individually, and we established a protocol to adequately resolve volatile Se species by capillary gas chromatography with mass selective detection (GC-MS). In addition, we synthesized and verified dimethylselenoniopropionate (DMSeP), a putative intermediate in the volatilization of inorganic Se by plants. Finally, we collected volatiles from Indian mustard and hybrid poplar plants grown in soil containing varying concentrations of selenate, selenite, and DMSeP. In preliminary experiments, we detected only minor amounts of the volatile Se-compound dimethylselenide (DMSe) from Indian mustard plants exposed to varying concentrations of each Se substrate. Hybrid poplar plants produced significant amounts of DMSe when grown in soil containing 100 mg/kg DMSeP (Figure 4). However, more DMSe was detected in identical chambers containing soil only (no plant). Future efforts will focus on (1) developing improved techniques for the collection of plant volatiles and (2) developing GC/MS methods to analyze seleno-amino acids from plants. The knowledge gained from this work will add to our understanding of Se-resistance in plants and could be used to enhance plant-based remediation of Se form polluted sites.