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Author ORCID Identifier


Campus-Only Access for Five (5) Years

Document Type


Degree Name

Doctor of Philosophy (PhD)

Degree Program

Plant, Soil & Insect Sciences

Year Degree Awarded


Month Degree Awarded


First Advisor

Om Parkash Dhankher

Second Advisor

Jason S. White

Third Advisor

Elsbeth Walker

Fourth Advisor

Masoud Hashemi

Subject Categories

Agricultural Science | Biotechnology | Molecular Biology | Molecular Genetics | Plant Biology | Plant Breeding and Genetics


The study explores plant defense against toxic metal stress, particularly focusing on glutathione (GSH) homeostasis via γ-glutamyl cycle. GSH, a potent antioxidant, plays a central role in maintaining redox balance, defense responses, and nutrient reserves in plant cells. Understanding the regulation of GSH degradation via γ-glutamyl cyclotransferases (GGCTs) and oxoprolinase (OXP1) is vital, especially under toxic metal stresses. Building upon prior research, which highlighted the role of AtGGCT2;1 in enhancing tolerance to arsenite (AsIII) toxicity in Arabidopsis, this study explores the contributions of two other GGCTs - AtGGCT1 and AtGGCT2;2, for their roles in GSH degradation and toxic metal tolerance. AtGGCT1 overexpression (OE) improves tolerance to arsenite (AsIII), cadmium (Cd), and mercury (Hg) by enhancing GSH degradation and subsequent recycling of constituent amino acids via the γ-glutamyl cycle. Whereas AtGGCT2;2 OE primarily enhances Cd tolerance. ggct1 and ggct2;2 mutants showed improved growth on vi AsIII and Cd. Further, ggct1 mutants had decreased As, Cd and Hg accumulation in shoots, but the results for roots varied. No difference was noticed in toxic metal accumulation in OE lines, but the OE lines had relatively better Glu recycling, as indicated by labeled 15N-glutamte analysis. The results from Arabidopsis were successfully translated into Camelina sativa, a biofuel crop. An AtGGCT2;1 homolog from Camelina, CsGGCT2;1, was overexpressed in Camelina and the modified plants showed strong tolerance to AsIII with 40-60% reduced As accumulation in roots and shoots. Additionally, the research investigates the role of AtOXP1 in GSH homeostasis and Glu recycling under As and Hg stress. The oxp1 T-DNA mutants exhibit lower Glu levels and susceptibility to Hg, but not to AsIII. The AtOXP1 OE enhanced tolerance to AsIII and Hg by promoting Glu recycling, lower lipid peroxidation and reduced As and Hg accumulation. AtOXP1 OE lines had better growth under low N conditions relative to WT, indicating enhanced internal Glu recycling. The findings have broad implications for future agriculture, food security, and development of metal-resilient crops for cultivation of contaminated lands. By comprehending the intricate interactions between plant genes, heavy metals, and nitrogen assimilation, this research contributes to a safer and more sustainable food production system.


Available for download on Saturday, February 01, 2025