Effects of organic acids on paraquat activity in maize

Abstract

In our previous study (Yoon et al., 2011, Pesticide Biochem. Physiol. 99: 65–76), we found that the level of foliar injury from paraquat (PA) in squash was generally less prevalent in younger leaves than in older ones. In addition, another previous study (Hyun et al., 2012, Korean J. Weed Sci. 32: 211–221) showed that the substance responsible for PA detoxification in young squash leaves was likely malic acid. Therefore, this study was conducted to investigate the effects of various organic acids on PA activity in maize. The levels of citric acid and malic acid in the fourth leaves were consistently higher than those in the first leaves in control and PA-treated leaves in both cultivars. In contrast, the level of tartaric acid in the first leaf was consistently higher than that of the fourth leaf in control and PA-treated leaves in both cultivars. Leaf injuries did not appear in maize treated with PA + malic acid at 0.3, 0.5, or 1%, PA + oxalic acid at 0.1, 0.3, 0.5, or 1%, PA + citric acid at 0.1, 0.3, 0.5, or 1%, or PA + tartaric acid at 1%. However, leaf injuries were observed in 69–82% of maize plants treated with 100 μM PA alone. The relative water contents in maize leaves were not reduced by PA + organic acid treatments compared with 100 μM PA treatment alone. Moreover, the superoxide and H2O2 contents in maize were significantly reduced by PA + most organic acids at various concentrations compared with 100 μM PA treatment alone. Moreover, MDA production in maize was significantly reduced by PA + organic acid treatments (except for PA + succinic acid) when compared with 100 μM PA treatment alone. Generally, chlorophyll contents in maize were not affected by treatment by PA alone or PA + organic acid. Taken together, these results suggest that squash plants contain organic acids such as malic acid and citric acid, which could nullify PA activity.