Growth inhibition of Pontederia crassipes to imidazolinones herbicides-group exposure.

ALS-inhibiting imidazolinone herbicides are widely used for selective weed control in Clearfield^® cropping systems. However, their physicochemical properties promote dispersion into adjacent aquatic environments, posing risks to non-target organisms such as aquatic macrophytes. This study aimed to elucidate the toxicological effects of the commercial formulation Kifix^® (a mixture of imazapyr and imazapic) on Pontederia crassipes, with emphasis on its biochemical and physiological responses. Two experiments were conducted using herbicide concentrations ranging from 0.2-1.0 mg L^-1, alongside untreated controls. Multiple parameters were evaluated in leaves and roots at 7 and 14 days after application, including visual symptoms, chlorophyll index, growth parameters, chlorophyll a fluorescence, gas exchange, epidermal anatomy, reactive oxygen species, lipid peroxidation, electrolyte leakage, antioxidant enzyme activity, glycolate oxidase, glutathione S-transferase, and acetolactate synthase activity, as well as carbohydrate, amino acid, and protein content. Upon exposure, mature leaves exhibited photochemical impairment, compromising carbon assimilation and photorespiration, and leading to carbohydrate accumulation. Stomatal aperture and conductance were also negatively affected. Oxidative stress responses and antioxidant enzyme activity changed in both leaves and roots. Notably, acetolactate synthase activity increased in treated plants, while protein and amino acid contents remained unchanged. Overall, Kifix^® significantly impaired P. crassipes, particularly by inhibiting the development of new tissues-such as leaves and plantlets essential for reproduction and spread-while also triggering physiological and biochemical disturbances in mature tissues.