Banca de DEFESA: GABRIELA DE SOUZA DA SILVA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : GABRIELA DE SOUZA DA SILVA
DATE: 08/01/2025
TIME: 08:00
LOCAL: online
TITLE:

Elucidation of the Mechanism of Action of the Herbicide Napropamide

KEY WORDS:

MoA, Protein biosynthesis, Rubisco, Glycolysis, Krebs cycle, Respiratory chain, Fermentation, Alcohol dehydrogenase.

PAGES: 81
BIG AREA: Ciências Agrárias
AREA: Agronomia
SUBÁREA: Fitotecnia
SPECIALTY: Matologia
SUMMARY:

Herbicides delay or inhibit plant growth by interfering with their biochemical and physiological processes and can be classified in various ways. However, the classification based on the mechanism of action is the most important, as it represents the first metabolic point in plants where the herbicide will act. The objective of this study was to elucidate the mechanism of action of the pre-emergent herbicide napropamide. The conducted steps included: proteomic analysis (label-free); metabolism assays evaluating variables such as alcohol dehydrogenase (ADH), phosphoenolpyruvate carboxylase (PEPC), phosphopyruvate hydratase (enolase), aconitase hydratase; accumulation of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂); and seed respiration. All experiments were performed under controlled conditions in a B.O.D. incubator (20 ºC / 8 hours light). Wheat seeds (Triticum aestivum L.) were used, treated with napropamide herbicide (1,260 g a.i.), s-metolachlor (2,880 g a.i.), and a control (distilled water), in addition to seeds with no treatment (no germination). For the respiration analysis, additional treatments included cold storage (maintained at low temperatures) and the herbicide sulfentrazone (800 g a.i.). The assays were conducted with 3 to 5 biological replicates, and samples were collected from 0 to 4 days after treatment, depending on the objective of each analysis. For respiration analysis, the CheckPoint O₂/CO₂ gas analyzer (PBI Dansensor) was used to measure CO₂ (%) over 4 days. Proteomic analysis revealed that napropamide affected five main metabolic pathways: protein biosynthesis, glycolysis, alcoholic fermentation, the Calvin-Benson cycle, and the Krebs cycle. Proteins involved in the biosynthesis new proteins and the Calvin-Benson cycle were down-accumulated, while proteins related to glycolysis, the Krebs cycle, and fermentation were up-accumulated. Among the identified proteins, four enzymes were selected for activity assays. ADH (fermentation), which was up-accumulated in the proteomic analysis, showed an activity increase of over 100% on the third day in seeds treated with napropamide. PEPC showed no statistically significant differences among treatments over the four days evaluated. On the other hand, enolase and aconitase (Krebs cycle), also up-accumulated, exhibited activity increases of 59% and 52%, respectively, on the third day of evaluation. Quantification of oxidative stress did not indicate significant differences among treatments. Proteomic analysis for the s-metolachlor herbicide identified 382 differentially expressed proteins, while napropamide resulted in only 99 differentially expressed proteins. Additionally, the respiration assay showed that napropamide treatment reduced the CO₂ production rate in seeds, indicating suppression of respiratory metabolism. The results suggest that the herbicide napropamide mainly impacts protein biosynthesis, triggering alterations in essential metabolic pathways such as cellular respiration. This effect induces a hypoxia-like metabolic state, activating adaptive mechanisms, including increased fermentation and ADH activity, to sustain basic energy processes. Confirmation of this hypothesis requires the completion of final experiments (gel proteomics, isocitrate dehydrogenase activity, quantification of amino acids, ethanol, and pyruvate), which will further complement the understanding of the herbicide’s mechanism of action and its metabolic consequences in plants.

COMMITTEE MEMBERS:
Interno - 1905333 - AROLDO FERREIRA LOPES MACHADO
Presidente - 2466219 - CAMILA FERREIRA DE PINHO
Externa à Instituição - CRISTINA MOLL HUTHER - UFF
Externa à Instituição - JÉSSICA FERREIRA LOURENÇO LEAL
Interna - ***.210.947-** - MARCIA SOARES VIDAL - EMBRAPA