Date of Award


Degree Name

Doctor of Philosophy




Jorge Gardea-Torresdey


The foliar application of nanomaterials as a method to overcome abiotic stress is relatively new compared to their use as fertilizers or pesticides in agricultural practice. It is also vital to understand the interface between leaf and nanomaterials, as nanomaterials might translocate into crop edible tissues, thus, causing potential toxicity in living beings during food consumption. In this dissertation, salt-stressed Capsicum annuum L was exposed to manganese (Mn) -based nanomaterials (Mn2O3 nanoparticles (MnNPs) and graphene quantum dots doped with Mn (GQD-Mn)) at different stages (seed germination and full life cycle). The dissertation focuses on investigating the mechanism of how Mn-based nanomaterials interact with C. annuum L. leaf, thus explaining the nanomaterial alleviation effect in salt stress. First, we primed C. annuum L. seeds with MnNPs and then performed critical comparisons in physiological parameters between nano-treated and control groups that are germinated under salt stress. We then investigated the plant stress-responsive indexes such as antioxidant gene expression and elemental redistribution. The work suggested that the MnNPs offset the adverse effects in root elongation caused by salt stress without disturbing those stress-responsive indexes. We attribute this to slow-released Mn ions due to the formation of nanoparticle-corona complex on the interior surface of the seed coat, which was observed by scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). Second, we conducted a comprehensive characterization of MnNPs and achieved in-situ tracking of the MnNPs in C. annuum L. leaf using spectral and electron microscopy imaging. This effort yielded the findings of MnNPs internalization on the leaf surface, MnNPs translocation within leaf tissue, and MnNPs-induced autophagy in leaf cells. This is an important finding as it provided a mechanistic view of MnNPs uptake in the leaf. It also suggested the potential of MnNPs in combating plant salt stress by sufficient storage of MnNPs and slow releasing of Mn ions. Lastly, we foliar applied GQD-Mn on salt-stressed, fully full-grown C. annuum L. and then observed both positive and negative effects. GQD-Mn alleviated salinity-driven reduction in C. annuum L. fruit, but also disturbed the synthesis of leaf epicuticular wax. Particularly, the ratios of long-chain normal alkanes were increased, which was detected by GC-MS. We attribute the double-edged effect to the unique optical properties of GQD-Mn, whereas the materials increased the light usage of C. annuum L. leaf but also caused heat-like stress. Overall, this dissertation provides a mechanistic perspective on nano-plant interaction and assesses the potential application of Mn-based nanomaterials in crop stress management.




Received from ProQuest

File Size

145 p.

File Format


Rights Holder

Yuqing Ye

Available for download on Monday, October 07, 2024