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Author ORCID Identifier

N/A

AccessType

Open Access Dissertation

Document Type

dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Plant, Soil & Insect Sciences

Year Degree Awarded

2016

Month Degree Awarded

September

First Advisor

Om Parkash Dhankher

Second Advisor

Baoshan Xing

Third Advisor

Dong Wang

Subject Categories

Agricultural Science | Plant Sciences

Abstract

The potential risks from metal-based nanoparticles (NPs) in the environment have increased with the rapidly rising demand for and use of nano-enabled consumer products. Plant’s central roles in ecosystem function and food chain integrity ensure intimate contact with water and soil systems, both of which are considered sinks for NPs accumulation. Thus, this dissertation describes three main objectives to comprehensively understand the interactions between plants and NPs and to characterize the role of glutathione (GSH) in detoxification of metal-based NPs in plants at physiological, biochemical, and molecular levels. (1) The effects of cerium oxide (CeO2) and indium oxide (In2O3) NPs exposure on Arabidopsis thaliana were investigated. In this study, we used the model plant “A. thaliana” to test the toxicity of two commonly used NPs, CeO2 and In2O3, in semisolid medium and hydroponic system. The results indicated that CeO2 NPs could induce oxidative stress in A. thaliana. The lipid peroxidation in terms of MDA contents and ROS production were very high in CeO2 and In2O3 treated plants. Activities of ROS scavengers and stress related enzymes in CeO2 and In2O3 NPs treated A. thaliana were also higher than control plants. Relative expression of genes involved in stress response such as the sulfur assimilation and GSH metabolic pathway demonstrated that A. thaliana activated the defense mechanism to counteract nanotoxicity. (2) To explore whether the enhanced level of GSH could protect plants from silver (Ag) NPs toxicity, we used the engineered Crambe abyssinica (a member of rassicaseae) plants expressing the E. coli γ-glutamylecysteine synthase (γ-ECS) gene. Our results showed that transgenic lines, when exposed to Ag NPs and AgNO3 (Ag+ ions), were significantly more tolerant in terms of fresh biomass, total chlorophyll contents, transpiration rates. MDA contents were much lower than the wild type (WT) plants. In addition, transgenic γ-ECS lines could accumulate 2-6 folds Ag in shoot and slightly lower or no difference in root relative to WT plant. These results indicate that GSH and related peptides protect plants from Ag nanotoxicity. (3) The third aim was to investigate the physiological effects of Ag NPs on soybean and to characterize the role of GSH in detoxification of Ag NPs and enhancement of nitrogen assimilation. Our results showed that the presences of Ag NPs could severely compromise the nitrogen fixation via symbiotic relationship in soybean. The total number of nodules and Rhizobium sp. growth in HM medium were inhibited upon exposure to Ag NPs. Elemental analysis indicated that Ag NPs mainly accumulated in the root system, and more than 50% Ag was in form of Ag-GSH, and the rest part remained in Ag NPs. The additions of GSH could notably counteract Ag nanotoxicity and enhance total N levels in soybean. Thus, plant might utilize GSH as a nitrogen source and might need very less help from the symbiotic relationship with Rhizobium sp. to assimilate the N. The related work is currently underway to further investigate the role of GSH in metal detoxification and N enhancement.

DOI

https://doi.org/10.7275/8991965.0

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