Date of Award

2022-08-01

Degree Name

Doctor of Philosophy

Department

Chemistry

Advisor(s)

Jorge L. Gardea-Torresdey

Abstract

In the present study, Zea mays seedlings grown under nano Cu(OH)2 (nCu), bulk Cu(OH)2 (bCu), and ionic CuSO4 (iCu) compound exposure were harvested after six days. The nutritional profile was determined to be significantly disrupted in the roots by 1000 ppm bCu treatment, resulting in a 58.7% reduction in potassium compared to the control. In the shoots, a significant decrease of manganese was observed for 10 and 1000 ppm iCu treatments with 55.7% and 64.2% reductions, respectively. The overall protein content and catalase (CAT) enzymatic activity, however, remained unaffected in either roots or shoots, while an absence of polyphenol oxidase (PPO) activity was observed for all samples. The genetic expression of defense-related genes, metallothionein (MT), CAT, ascorbate peroxidase (APX), and PPO was assessed. The genetic expression of MT was upregulated 50-fold in roots treated with 1000 ppm bCu. There were no significant differences in CAT transcripts among the various treatments, while APX was upregulated 28 and 19-fold in shoots treated with 10 ppm bCu and 10 ppm nCu, respectively. Meanwhile, APX mRNA levels were downregulated five-fold in shoots treated with 1000 ppm iCu. Thus, indicating that the role of APX in plant defense was reinforced in seedlings exposed to low concentration of particulate Cu compounds. Remarkably, no PPO expression was found in any of the treatments and controls, which suggests this enzyme is expressed only under specific external factors or seedlings have an â??immatureâ?? cascade signaling activation of the PPO system. Taken together, these results show that bCu and nCu treatments at a low concentration do not compromise vital cell machinery but rather elicit the enhancement of defense responses as observed through the increase in APX expression. Furthermore, under optimal concentrations, these Cu treatments show promise in enhancing corn defense responses, which can ultimately lead to increases in future global crop yields. The dissolution of nano CuO (nCuO) in nutrient solution was monitored over time using single particle ICP-MS, to measure particle diameter based on mass determinations of Cu containing particles. From the introduction of nCuO into the nutrient solutions to week three, 50ppm 80nm nCuO, 100ppm 80nm nCuO 50ppm 40nm nCuO had dissolution percentages of 28%, 22% and 20%, respectively. Under the same dissolution conditions in the presence of corn seedlings, these dissolution percentages were considerably reduced to 18%, 16% and 15%, respectively, confirming that nCuO transformation over time is directly related to direct matrix conditions. Furthermore, all the nCuO treatments significantly reduced the root lengths and biomass, when compared to control. All 100ppm treatments significantly hindered shoot mass and only the 100ppm 80nCuO treatment significantly reduced shoot length, when compared to control. Meanwhile, chlorophyll content remained unaffected when compared to the control. These findings suggest that nCuO has an effect on biological tissues that have direct contact with these particles. If utilized for agricultural applications their transformation and gradual release of Cu2+ to the environment should be thoroughly monitored to balance nutritional quality and prevent cytotoxicity.

Language

en

Provenance

Received from ProQuest

File Size

94 p.

File Format

application/pdf

Rights Holder

Carolina Valdes Bracamontes

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