ARS | Publication request: Study of the effects of chromium exposure on sulfur metabolic pathways in the model plant Medicago truncatula

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 20, 2006
Publication Date: October 26, 2006
Citation: Montes-Holguin, M.O., Peralta-Videa, J.R., Parsons, J.G., Grusak, M.A., Gardea-Torresdey, J.L. 2006. Study of the effects of chromium exposure on sulfur metabolic pathways in the model plant Medicago truncatula [abstract]. In: Society for Advancement of Chicanos and Native Americans in Science 2006 National Conference, October 26-29, 2006, Tampa, Florida. Paper No. G48, p. 161.

Technical Abstract: Chromium is a common contaminant that is more toxic as hexavalent species [Cr(VI)] than trivalent species [Cr(III)]. Some plants absorb chromium and reduce Cr(VI) to Cr(III), yet the uptake and reduction mechanisms are still unknown. Sulfur is a constituent of two essential amino acids and plays an important role in the natural sulfur cycle. Sulfur uptake in plants is inhibited by other divalent anions such as chromate. This research aims at studying the effects of chromium in the sulfur metabolic pathways. Medicago truncatula, a model plant for genomic research, was chosen for this study because there is information on putative sulfate transporters for this plant. The accumulation and reduction of chromium and its effects on nutrient uptake and sulfur metabolism were studied by inductively coupled plasma optical emission spectroscopy, X-ray absorption spectroscopy, and ATP sulfurylase assays, respectively. Plants were exposed to varying concentrations of chromate, harvested, and analyzed. Ex-vivo enzyme activity assays for ATP-sulfotransferanse activity (E.C. 2.7.7.4) were performed to determine the enzyme response to chromate. The results show that plants exposed to 40 mg/L of Cr(VI) absorbed 2267, 1038, and 505 mg Cr/kg in roots, stems, and leaves, respectively. Sulfur uptake increased from 987 mg/kg in control roots to 1457 mg/kg in roots exposed to 40 mg/L of Cr(VI). XAS results showed a reduction of Cr(VI) to Cr(III) inside the plant, and ATP sulfurylase activity increased in sulfur starved plants, as compared to plants exposed to 44 uM of sulfur. Gene expression results will be discussed.