Effects of malic acid on paraquat and environmental stresses in maize

Abstract

This study was conducted to evaluate the effects of various organic acids on the reduction of paraquat activity in maize. The authors studied the level of leaf injury in maize when exposed to other stressors such as drought, low temperature and oxyfluorfen. At 1, 2 and 3 days after a 100 μM paraquat treatment, 69–73% of maize plants showed leaf injuries. However, 27–40% of maize plants showed leaf injury when first treated with malic acid at a 0.5% concentration and then, 24 h later, with a 100 μM paraquat treatment. In other studies, paraquat treatments were applied first, and then followed by malic acid treatments. The authors applied a 100 μM paraquat treatment and then, 24 h later, applied a 0.5% concentration of malic acid. In these cases, leaf injuries were not significantly different. In our studies using other organic acids, our control seedlings were treated exclusively with 100 μM of paraquat. Compared with our control, leaf injuries were reduced by 15% in response to a 0.5% concentration of tartanic acid followed by a 100 μM paraquat treatment. They also observed a 26% reduction of leaf injuries when a 0.5% concentration of citric acid was followed by a 100 μM paraquat treatment. A greater reduction was observed in leaf injuries when organic acids (0.5% concentrations) were applied at the same time as paraquat. Compared to the control, leaf injuries were reduced by 35% after a tartanic acid-PA treatment, 56% after an oxalic acid-PA treatment and 61% after a citric acid-PA treatment. Malic acid did not alter the activity of oxyfluorfen. This may be due to the fact that oxyfluorfen had a different mode of action than paraquat. Pre-treatment using malic acid did not reduce damage caused by cold and drought stress. In conclusion, it was found that the order in which malic acid and paraquat were applied produced different leaf injury reduction rates. Leaf injury was most effectively reduced when malic acid was either applied before paraquat or at the same time. In cases where malic acid was applied after paraquat, there was no significant reduction in leaf injury.