Chlorpyrifos and Imidacloprid Phytotoxicity Triggers Oxidative Stress and Hinders Lettuce Growth, Cellular, and Metabolic Functions

Abstract

Overuse of pesticides often poses a severe threat to agricultural productivity. In vitro experiments were conducted to assess the effect of different concentrations (10, 20, 40, 80, and 100 μg mL-1) of chlorpyrifos (CP) and imidacloprid (IMD) on germination, physiology, and cellular properties of lettuce (Lactuca sativa). The 100 μg mL-1 dose greatly reduced germination attributes, length, and seedling survival. At 100 μg mL-1, CP and IMD decreased seed germination (80% and 60%), vigor indices (76.7% and 65.3%), survival (79.5% and 65.5%), and tolerance indices (83.3% and 62.5%) as compared to control. Insecticide-exposed roots showed cracks/fractures, disintegration, and distortion over control roots, thus exhibiting the toxic potential of insecticides. Elevated CP and IMD concentrations led to increased oxidative stress and the generation of reactive oxygen species (ROS) in lettuce seedlings. When subjected to 100 μg mL-1 of CP and IMD, seedlings exhibited a significant (p ≤ 0.05) increase in levels of hydrogen peroxide (70.2% and 56.8%), superoxide radicals (88.9% and 70.5%), electrolyte leakage (87.9% and 66.4%), and malondialdehyde (94.5% and 61.4%). Furthermore, insecticide dose-dependent declines in adenosine triphosphate (ATP) content and respiration efficiency (RE) were observed in seedlings. Antioxidant enzymes' activity in lettuce was modulated by exogenous insecticide treatments. Secondary metabolites and antioxidant activities were altered in lettuce under insecticide stress. Both insecticides imparted phytotoxic effects that highlight the importance of their optimal utilization in soil-plant systems and their careful monitoring in soils. There is an urgent need to develop slow-release and target-specific pesticide formulations that ensure effective crop protection while safeguarding soil health.