Mancozeb associated with water deficit: Physiological and biochemical responses of soybean plants

Can oxidative stress from xenobiotics be intensified under water deficit conditions? Based on the hypothesis that the exposure to a xenobiotic aggravates the oxidative damages induced by water deficit, soybean plants were cultivated in pots eqquipped with soil water potential sensors to continuously monitor soil moisture levels. The experiment was conducted in 2020, in a protected environment, using a randomized block design with three replications. To comprehensively evaluate physiological and biochemical responses of plants, we conducted a range of analyses, including measurements of stomatal conductance, leaf temperature, chlorophyll, chlorophyll fluorescence, relative water content, membrane damage, electrical conductivity, lipid peroxidation, concentration of reactive oxygen species – hydrogen peroxide and superoxide, activity of antioxidative enzymes – ascorbate peroxidase, superoxide dismutase, catalase, non-enzymatic compounds – non protein thiols, nitric oxide and proline. Plants that received the application of the fungicide mancozeb showed 1 °C higher temperature compared to the control plants. Irrigated soybean plants had higher nitric oxide content when treated with mancozeb, but under water deficit the higher content was observed in control plants. No deleterious effects of mancozeb as a xenobiotic were observed when applied at the recommended dose for soybean cultivation, even under water deficit conditions. The plants exhibited deleterious effects caused by water deficit, particularly in relation to oxidative stress induced by water shortage. The combination of two stresses (water deficit and xenobiotics) did not result in the maximization of negative effects caused by water stress. By refuting the working hypothesis, it becomes evident that the application of mancozeb to plants under water deficit conditions did not exacerbate the damage induced by this stress. Responses to this combination are contingent upon various factors, including the stress duration, its severity, the plant species involved, and, in the case of xenobiotics, their inherent properties and mode of action within the plant.