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Effect of cerium oxide nanoparticles on rice: A study involving the antioxidant defense system and in vivo fluorescence imaging Cyren Rico, Jie Hong, Maria I Morales, Lijuan Zhao, Ana C Barrios, JianYing Zhang, Jose R Peralta-Videa, and Jorge L Gardea-Torresdey Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/es401032m • Publication Date (Web): 10 May 2013 Downloaded from http://pubs.acs.org on May 13, 2013
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Effect of cerium oxide nanoparticles on rice: A study involving the
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antioxidant defense system and in vivo fluorescence imaging
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Cyren M. Rico†£, Jie Hong‡, Maria Isabel Morales†, Lijuan Zhao†£, Ana Cecilia Barrios†,
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Jian-Ying Zhang§, Jose R. Peralta-Videa†£, Jorge L. Gardea-Torresdey*†£
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Department of Chemistry, The University of Texas at El Paso, 500 W. University Avenue, El Paso Texas 79968, United States
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Paso, 500 W. University Avenue, El Paso Texas 79968, United States
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Department of Biological Sciences, Border Biomedical Research Center, The University of Texas at El Paso, 500 W. University Avenue, El Paso Texas 79968, United States
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Environmental Science and Engineering PhD Program, The University of Texas at El
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University of California Center for Environmental Implications of Nanotechnology (UC CEIN), The University of Texas at El Paso
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Corresponding author:
[email protected] (J. Gardea)
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Abstract: Previous studies have reported the uptake of cerium oxide nanoparticles
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(nCeO2) by plants, but their physiological impacts are not well understood yet. This
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research was aimed to study the impact of nCeO2 on the oxidative stress and antioxidant
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defense system in germinating rice seeds. The seeds were germinated for 10 days in
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nCeO2 suspension at 62.5, 125, 250 and 500 mg L-1 concentrations. The Ce uptake,
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growth performance, stress levels, membrane damage and antioxidant responses in
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seedlings were analyzed. Ce in tissues increased with increased nCeO2 concentrations,
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but the seedlings showed no visible signs of toxicity. Biochemical assays and in vivo
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imaging of H2O2 revealed that, relative to the control, the 62.5 and 125 mg nCeO2 L-1
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treatments significantly reduced the H2O2 generation in both shoots and roots. Enhanced
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electrolyte leakage and lipid peroxidation were found in the shoots of seedlings grown at
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500 mg nCeO2 L-1. Altered enzyme activities and levels of ascorbate and free thiols
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resulting in enhanced membrane damage and photosynthetic stress in the shoots were
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observed at 500 mg nCeO2 L-1. These findings demonstrate a nCeO2 concentration-
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dependent modification of oxidative stress and antioxidant defense system in rice
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seedlings.
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Keywords: Antioxidative enzyme activity, Cerium oxide nanoparticles, Oxidative stress,
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Rice
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Introduction
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Engineered nanoparticles (ENPs) have varied technological applications in
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industrial, medical and agricultural products. The considerable amount of ENPs released
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to the ecosystem has brought about serious environmental concerns due to their possible
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toxic effects in living organisms, particularly plants.1-2 ENPs can induce modifications in
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the physiological and biochemical processes of plants that may have implications in their
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growth and seed production. This concern has brought about a fast growing research
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interest in the plant-ENP interactions.
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Recent reviews documented that studies on plant-ENP interactions have focused
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on the uptake, accumulation, translocation and speciation of ENPs and its toxic effects on
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seed germination and seedling growth.1-2 The same reviews revealed limited studies
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dealing with the biochemical and molecular changes induced by ENPs and their
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implications on ENPs phytotoxicity. Studies exploring this knowledge gap would be
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useful for a better understanding of plant-ENP interactions.3
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Biochemical studies have shown that ENPs influence the antioxidative enzyme
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activity,4-7 photosynthetic processes,8-10 oxidative stress,11-13 and DNA expressions 14-16 in
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plants. However, further studies are still needed to draw a comprehensive picture of the
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plant-ENP interactions at the biochemical or molecular level.
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nCeO2 are extensively used in chemical mechanical planarization and fuel
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additives.17-18 These NPs are stable and undergo a very limited dissolution in
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environmental media and plant tissues.19-21 Cornelis et al.19 reported a dissolution
