Inhibitory Effect of 3-Cyanobenzoic Acid on Initial Growth of Maize Seedlings and Its Biochemical Impacts on Antioxidant and Energy Metabolisms

The discovery of new herbicides is one of the most significant challenges of modern agriculture. Estimates indicate that for every 200,000 molecules assessed, only one will have promising characteristics. We evaluated the effects of 0, 125, 250, 500, 1000, 1500, 2000, and 2500 µM 3-cyanobenzoic acid, a synthetic compound derived from benzoic acid, on the growth and antioxidant and energy metabolism of maize seedlings grown in a hydroponic medium for 96 h. The root length and fresh and dry weights of roots and leaves were significantly reduced by 3-cyanobenzoic acid, probably due to increased reactive oxygen species (ROS) generation. In contrast, the activities of peroxidase, catalase, and superoxide dismutase were stimulated in roots. Increases in potassium cyanide (KCN)-sensitive and salicylhydroxamic acid (SHAM) respiration were evident in the root apexes. Interestingly, the ATP contents were up to 2-fold greater in the treated roots than in the control roots. However, 3-cyanobenzoic acid did not influence oxygen consumption by isolated mitochondria when succinate and/or L-malate were used as substrates. Altogether, our data suggest that 3-cyanobenzoic acid reduces the growth of maize seedlings through the induction of oxidative stress. The stimulation of respiration sensitive to SHAM was due to the electron drain of the cytochrome oxidase (COX) pathway to the alternative oxidase pathway (AOX), with a consequent increase in ROS production. In addition, 3-cyanobenzoic acid should stimulate respiration sensitive to KCN (via cytochrome oxidase, COX) and AOX indirectly by a mechanism not yet known.