Disruption of plant cell division by methoxychalcones and cinnamaldehyde: insights into their herbicidal mode of action.

Weed control is crucial for global food production, as weeds cause economic losses. Chalcones are multifunctional compounds with diverse molecular targets, strong phytotoxic potential, and easy synthesis. This work investigated the herbicidal potential and mode of action of methoxychalcones, as well as their precursor, cinnamaldehyde. Herbicidal activity was assessed via dose-response curves at 0-100 µmol L- 1. Mode of action experiments included phenylalanine ammonia lyase (PAL) activity, electrolyte leakage, chlorophyll a fluorescence, photosynthetic oxygen evolution, and mitotic index. Results were evaluated using ANOVA with Tukey's test and Kruskal-Wallis with Dunn's test (p < 0.05). Non-linear regression assessed dose-response curves. 4'-hydroxy-3'-methoxychalcone (CH1) was the most potent compound, with an IC50 of 17.3 µmol L- 1 in Arabidopsis thaliana. Cinnamaldehyde (P1) and 3,4-dimethoxychalcone (CH2) had IC80 values close to 100 µmol L- 1, whereas the chalcone 4'-hydroxy-3'-methoxychalcone (CH1) had IC80 of 56.1 µmol L- 1. Both chalcones and their precursor induced elongated cell morphology and resulted in a reduced proportion of cells progressing through mitotic phases, particularly those observed at the metaphase stage during cell division. Methoxychalcones disrupt cell division, resulting in abnormal plant growth and development. Through disruption of the cell cycle, these compounds impair new tissue formation and consequently reduce overall plant growth.