Comparative Analysis of Antioxidant Pathways in Plant vs. Animal Tissues

Thesis Abstract

Chronic imbalances in antioxidant defenses across biological kingdoms threaten cellular homeostasis and are implicated in diverse pathophysiological processes; however, comparative insights into the regulation, capacity, and integration of antioxidant pathways in plant and animal tissues remain fragmented, limiting cross-kingdom translational applications. This study aims to systematically compare antioxidant pathways in representative plant and animal tissues to elucidate shared and divergent regulatory mechanisms, with a focus on how these pathways respond to oxidative challenge and contribute to redox homeostasis. The specific objectives are (i) to quantify and compare the envelope of enzymatic and non-enzymatic antioxidants (superoxide dismutase, catalase, ascorbate peroxidase in plants; SOD, catalase, glutathione peroxidase in animals, plus ascorbate and glutathione pools) under induced oxidative stress; (ii) to evaluate transcriptional and post-translational regulation of key antioxidant enzymes using targeted proteomics and qPCR; (iii) to assess the contribution of non-enzymatic antioxidants (ascorbate, glutathione, phenolics in plants, uric acid in animals) to overall redox buffering via correlation and regression analyses; and (iv) to synthesize findings within two theoretical frameworks—the oxidative stress theory and the resource allocation/oxidative cost framework—to identify convergent strategies and trade-offs across kingdoms. The study employs a comparative, cross-sectional design conducted in controlled laboratory settings. The population comprises mature leaves from Arabidopsis thaliana and liver tissue from Mus musculus as representative plant and animal tissues, respectively. A sample size of n=30 per tissue type provides adequate power to detect medium effect sizes (d=0.5) at ?=0.05 with 80% power, using a balanced factorial framework. Induced oxidative stress is simulated through exposure to 0, 200, and 400 ?M H2O2 for 6, 12, and 24 hours to generate dose- and time-dependent redox responses. Data collection integrates biochemical assays, molecular analyses, and spectroscopic measurements spectrophotometric quantification of SOD, catalase, and peroxidase activities; high-performance liquid chromatography (HPLC) quantification of reduced and oxidized glutathione (GSH/GSSG) and ascorbate; LC-MS/MS-based targeted proteomics for antioxidant enzymes; RT-qPCR for transcript levels of redox-related genes; and untargeted metabolomics to capture phenolic and thiol-based antioxidants. Data validity is enhanced through calibration curves, internal standards, technical duplicates, and cross-validation of transcript and protein abundance. Analytical methods include repeated-measures ANOVA to compare tissue types across stress levels and time points, multivariate regression to identify predictors of redox state (GSHGSSG ratio, ascorbate redox status), and structural equation modeling to test the proposed theoretical frameworks linking stress exposure, antioxidant capacity, and redox outcomes. A conceptual model will be tested to delineate causal pathways among enzymatic activities, non-enzymatic antioxidant pools, and redox homeostasis, with sensitivity analyses addressing potential confounders such as tissue-specific baseline antioxidants. The expected findings anticipate that plants exhibit a more robust non-enzymatic antioxidant reservoir and higher phenolic contributions, while animals rely more on constitutive enzymatic defenses; however, both groups will show upregulation of core enzymes under oxidative challenge, with tissue- and time-dependent modulation patterns. The study also anticipates differential regulatory signatures at the transcriptional and translational levels, reflecting kingdom-specific allocation strategies under stress. This research contributes to knowledge by providing a unified, cross-kingdom profile of antioxidant defense architecture, clarifying how plants and animals optimize redox balance under stress, and identifying conserved versus divergent regulatory nodes. It offers empirical evidence to refine the oxidative stress theory in cross-kingdom contexts and informs broader discussions on resource allocation and oxidative costs in evolutionary biology. Practical implications include informing crop improvement strategies aimed at enhancing stress tolerance through antioxidant pathway engineering and guiding biomedical approaches to modulate redox balance in liver-related diseases. Limitations include the use of a single animal tissue and a single plant species, which may constrain generalizability; future work should extend to diverse tissues and species, incorporate in vivo stress models, and explore longitudinal dynamics. Recommendations emphasize expanding comparative analyses across additional taxa, integrating omics data for holistic redox network reconstruction, and evaluating functional outcomes such as stress tolerance and metabolic efficiency under chronic oxidative pressure.