Toxicity of Arsenic (III) and (V) on Plant Growth, Element Uptake, and Total Amylolytic Activity of Mesquite (Prosopis Juliflora x P. Velutina)

Abstract

The effects of arsenite [As(III)] and arsenate [As(V)] on the growth of roots, stems, and leaves and the uptake of arsenic (As), micro- and macronutrients, and total amylolytic activity were investigated to elucidate the phytotoxicity of As to the mesquite plant (Prosopis juliflora x P. velutina). The plant growth was evaluated by measuring the root and shoot length, and the element uptake was determined using inductively coupled plasma optical emission spectroscopy. The root and leaf elongation decreased significantly with increasing As(III) and As(V) concentrations; whereas, stem elongation remained unchanged. The As uptake increased with increasing As(III) or As(V) concentrations in the medium. Plants treated with 50 mg/L As(III) accumulated up to 920 mg/kg dry weight (d wt) in roots and 522 mg/kg d wt in leaves, while plants exposed to 50 mg/L As(V) accumulated 1980 and 210 mg/kg d wt in roots and leaves, respectively. Increasing the As(V) concentration up to 20 mg/L resulted in a decrease in the total amylolytic activity. On the contrary, total amylolytic activity in As(III)-treated plants increased with increasing As concentration up to 20 mg/L. The macro- and micronutrient concentrations changed in As-treated plants. In shoots, Mo and K were reduced but Ca was increased, while in roots Fe and Ca were increased but K was reduced. These changes reduced the size of the plants, mainly in the As(III)-treated plants; however, there were no visible sign of As toxicity.

KEY WORDS:

• arsenic (As)
• phytoremediation
• amylase
• Prosopis
• mesquite

ACKNOWLEDGMENTS

The authors would like to acknowledge the National Institutes of Health (grant S06 GM8012-33) and the University of Texas at El Paso's Center for Environmental Resource Management through funding from the Office of Exploratory Research of the U.S. Environmental Protection Agency (cooperative agreement CR-819849–01). They also thank the HBCU/MI, Environmental Technology Consortium that is funded by the Department of Energy. J. Gardea-Torresdey acknowledges the National Institute of Environmental Health Sciences (grant R01ES11367-01) and the Dudley family for the Endowed Research Professorship in Chemistry. N.S. Mokgalaka-Matlala would like to thank the National Research Foundation of South Africa for funding her postdoctoral fellowship. The authors also thank the contributions of anonymous reviewers.