http://repositorio.ufc.br/handle/riufc/364 2026-04-09T23:05:05Z http://repositorio.ufc.br/handle/riufc/85557 Título: Plasticidade de cajueiros à baixa disponibilidade hídrica no solo: mecanismos fisiológicos, metabólicos e epigenéticos Autor(es): Costa, Igor Rafael Sousa Abstract: The cashew tree (Anacardium occidentale L.) is a highly relevant species for the Brazilian semi-arid region, which it develops under environmental conditions characterized by a combination of abiotic stresses, such as high irradiance, salinity, water deficit, and high temperatures. Adaptation to this environment involves physiological and molecular mechanisms that regulate acclimation to environmental stress. This thesis investigated the processes that support tolerance and the ability to adjust to water deficit in the cashew tree, integrating different biological levels to identify functional patterns associated with adaptation. In the first chapter, physiological, biochemical, metabolic, and molecular responses were evaluated in two contrasting cashew genotypes subjected to successive cycles of water deficit followed by rehydration. The BRS 226 genotype showed greater osmotic stability during stress, more efficient photosynthetic recovery, and greater functional adjustment capacity after repeated drought exposures. The regulation of the redox state and the progressive activation of the antioxidant system indicated physiological adjustment to recurrent stress, accompanied by extensive metabolic reorganization, with modulation of compounds associated with energy metabolism and cellular adaptation. In contrast, the CCP 09 genotype showed more restricted physiological and metabolic responses, with less recovery capacity after successive stress cycles. The differential modulation of the expression of genes associated with the stress response and the activation of markers re ated to DNA methylation during recovery suggest the participation of epigenetic mechanisms in the physiological reorganization induced by drought cycles. Taken together, the results indicate that the differential tolerance between genotypes is associated with the coordination between physiological, metabolic, and molecular adjustments in response to recurrent water stress. The second chapter investigated the epigenetic dynamics associated with a single water deficit event followed by recovery in cashew seedlings, using enzymatic sequencing of DNA methylation. Although the overall methylation profile remained relatively stable across water conditions, extensive local alterations were detected throughout the genome, indicating epigenetic reorganization associated with the plant's physiological state. These modifications were related to distinct regulatory and metabolic processes between stress and recovery phases, suggesting that DNA methylation participates in the functional modulation of the water response. The observed epigenetic variations accompanied changes in photosynthetic performance and the expression of marker genes, highlighting an association between epigenetic modulation and physiological adjustments to water deficit. In an integrated manner, the results demonstrate that the cashew tree's response to water deficit involves coordination between physiological, metabolic, and epigenetic processes that contribute to functional adjustments of metabolism and the photosynthetic apparatus during stress and recovery. These findings broaden the understanding of the regulatory mechanisms associated with the water response in tropical perennial species and provide a basis for the development of genetic improvement strategies and adaptive management under scenarios of greater climate variability. Tipo: Tese 2026-01-01T00:00:00Z http://repositorio.ufc.br/handle/riufc/85351 Título: Abordagem ômica integrada na investigação da aclimatação ao estresse salino induzida pela ativação do retículo endoplasmático em feijão-caupi (Vigna unguiculata [L.] Walp) Autor(es): Cavalcante, Francisco Lucas Pacheco Abstract: Salinity represents one of the main limiting factors for agricultural productivity, affecting ionic homeostasis, redox balance, metabolism, and plant growth. Although the endoplasmic reticulum (ER) is recognized as an important hub for integrating cellular signals under stress conditions, the mechanisms by which its activation can modulate salt tolerance in cowpea (Vigna unguiculata [L.] Walp.) remain incompletely understood. This thesis investigated whether the controlled stimulation of adaptive endoplasmic reticulum signaling, through transient activation of the unfolded protein response (UPR) induced by tunicamycin (TM), could function as a priming mechanism, increasing the efficiency of acclimation to salinity. Foliar application of TM was selected to induce systemic ER signaling without directly altering ion uptake by roots, allowing the controlled activation of adaptive pathways prior to salt exposure. An integrative and temporal approach was employed, combining physiological analyses, Na+ and K+ quantification, hydrogen peroxide (H2O2) determination, qPCR-based gene expression analysis of unfolded protein response (UPR) markers and ion transporters, as well as metabolomic, lipidomic, and quantitative proteomic analyses in leaves. The results demonstrated that TM priming significantly attenuated the deleterious effects of NaCl, promoting improved photosynthetic performance and enhanced plant growth. A reduction in Na+ accumulation in the shoot, greater K+ retention, and increased ionic sequestration in roots were observed, indicating improved ionic homeostasis. TM application induced a rapid and transient ER stress response, characterized by an initial increase in H2O2 and early expression of UPR-related genes, with a return to basal levels within 24 hours. Under salinity, plants previously treated with TM exhibited lower H2O2 accumulation, earlier and more efficient activation of pathways associated with ER signaling and sodium transport, as well as reduced expression of chaperones and Na+ transporters. Proteomic analysis revealed that salinity promoted broad metabolic repression, including reductions in enzymes of the Calvin cycle and glycolysis (GAPDH, triose phosphate isomerase) and in ribosomal proteins, whereas TM priming attenuated this suppression and promoted selective reinforcement of the translational machinery and proteins associated with stress adaptation. Metabolomic and lipidomic profiles indicated enhanced osmotic adjustment and membrane remodeling, reinforcing cellular stability under stress conditions. It is concluded that transient ER activation acts as a physiological preconditioning mechanism, coordinating redox regulation, proteostasis, ionic homeostasis, and metabolic reprogramming. These findings expand the understanding of the ER as a regulatory hub in plant adaptation to salt stress and highlight promising molecular targets for breeding strategies aimed at increasing cowpea resilience in salinized environments. Tipo: Tese 2026-01-01T00:00:00Z http://repositorio.ufc.br/handle/riufc/85031 Título: Hepatotoxicidade induzida pelo herbicida 2,4-D e seu metabólito 2,4-DCP: uma investigação mecanística integrando toxicologia de redes e análises em peixe-zebra Autor(es): Martins, Rafael Xavier Abstract: The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and its main environmental metabolite, 2,4-dichlorophenol (2,4-DCP), are emerging contaminants frequently detected in aquatic ecosystems. Although their hepatotoxicity in vertebrates is already recognized, the underlying molecular mechanisms remain poorly understood. Moreover, most studies employ high concentrations and acute exposures, limiting the understanding of effects under environmentally relevant conditions characterized by prolonged exposure to low concentrations. In this study, we adopted an integrated approach combining computational toxicology and in vivo experiments using zebrafish (Danio rerio) to investigate the mechanisms of liver toxicity induced by 2,4-D and 2,4-DCP, as well as their acute and chronic effects at environmentally relevant concentrations. Network toxicology and molecular docking analyses revealed potential interactions of both compounds with key proteins associated with liver toxicity, including SRC, AKT1, RXRA, HSP90AA1, and MDM2. Functional enrichment analyses (Gene Ontology and Reactome) indicated the involvement of critical signaling pathways, including nuclear receptors and PI3K/AKT, as well as biological processes associated with liver toxicity, such as oxidative stress, lipid accumulation, mitochondrial dysfunction, and cell death. In vivo assays demonstrated that environmentally relevant concentrations (3, 30, and 300 μg/L) induced acute liver toxicity in zebrafish larvae, corroborating the in silico predicted mechanismse. In adult fish, chronic exposure resulted in histopathological alterations, including lipid accumulation, cell death, and tissue disorganization, even at 30 μg/L of 2,4-D, corresponding to the maximum allowed value (MAV) for drinking water in Brazil. This study describes, for the first time, biological targets and molecular pathways associated with 2,4-D and 2,4-DCP-induced hepatotoxicity and demonstrates that environmentally relevant concentrations can disrupt essential cellular processes, leading to liver damage. These findings question the safety of the MAV of 2,4-D established by Brazilian legislation for non-target organisms and highlight the urgent need to include 2,4-DCP in environmental monitoring programs, as well as to reassess safe exposure limits for these contaminants. Tipo: Tese 2025-01-01T00:00:00Z http://repositorio.ufc.br/handle/riufc/83904 Título: Cell-type-specific metabolism in plants and metabolic plasticity of C3 and C4 leaves subjected to 13C labelling under dark and light conditions Autor(es): Morais, Eva Gomes Abstract: Plants with C3 and C4 metabolisms differ in biochemical, anatomical and physiological aspects. Several factors related to the photosynthesis of these two groups of plants have been well elucidated. However, the distribution of metabolic fluxes after CO2 assimilation is still poorly understood, especially regarding flux distribution through the tricarboxylic acid (TCA) cycle and associated metabolic pathways. Considering the primary role of nitrogen assimilation in plant growth and productivity, our hypothesis is that the greater photosynthetic efficiency of C4 plants can also be explained by a differential regulation of metabolic fluxes through the TCA and glutamine synthetase/glutamate synthase (GS/GOGAT) cycles. In this work, we conducted isotopic labelling experiments by subjecting leaves of C4 plants (maize and sorghum) and a representative species of the C3 group (cowpea) to 13C-HCO3 labelling in the absence and presence of light. The results reported that illuminated leaves of all species showed a significant increase in 13C-labeled metabolites, probably reflecting the activation and increase in the carboxylative activities of the enzymes ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and phosphoenolpyruvate carboxylase (PEPc), respectively. However, TCA cycle metabolites showed lower 13C enrichment in cowpea leaves in darkness and light. 13C positional labelling data on malate demonstrate that C4 plants have greater CO2 assimilation mediated by PEPc in light and darkness. According to our hypothesis, 13C enrichment in glutamate was higher in illuminated C4 plants than in cowpea, indicating that C4 plants have a higher carbon flux derived from PEPc activity towards the GS/GOGAT cycle in the light. Furthermore, metabolites related to the TCA cycle and associated pathways presented higher 13C enrichment in C4 plants, especially citrate, which showed enrichment in illuminated and dark exposed C4 leaves. Our results also highlight differences among C4 species. For example, in the presence of light, sorghum displayed higher 13C enrichment in sugars, while maize presented higher enrichment in malate and aspartate, indicating a differential carbon flux mode among C4 species. Our results suggest that C4 plants have greater metabolic flux through the TCA cycle under light and dark conditions and that the distribution of photosynthetic carbon throughout primary metabolism is species- and time-dependent, especially under light conditions. Tipo: Tese 2024-01-01T00:00:00Z