Sweet corn carotenoid concentrations influenced by herbicide applications

Carotenoids serve antioxidant functions in plant photosynthetic processes, as well as in actions of disease reduction in mammalian systems. Lutein and zeaxanthin are important dietary carotenoids in suppressing aging eye diseases. Age-related macular degeneration now affects more than 1.75 million individuals in the US. Sweet corn (Zea mays var. rugosa) is one of only a few vegetable sources high in zeaxanthin. Mesotrione herbicide is currently labeled for selective pre- and post-emergence weed control in sweet corn production. Mesotrione competitively inhibits phytoene desaturase, a critical enzyme in carotenoid biosynthesis, which results in bleaching of leaf tissues in susceptible species and eventual plant death. Sweet corn is tolerant to mesotrione applications; however, differing sensitivity exists among genotypes. What remains unclear is the impact of mesotrione on carotenoid concentrations in mature sweet corn kernels following post-emergent applications to young corn plants. Our research objective was to measure mature kernel carotenoid concentrations in response to post-emergence applications of mesotrione to genotypes of different sensitivities. Post-emergence treatments included mesotrione applied alone, or in mixtures with the photosystem II inhibitor atrazine applied to corn plants of either 5-10 or 15-20 cm in height. Kernels were harvested from mature plants and measured for carotenoid concentrations. Mesotrione applied alone, or in mixtures with atrazine acted to increase concentrations of kernel antheraxanthin, lutein, and zeaxanthin in several sweet corn genotypes. Mesotrione applications resulted in greater pools of kernel carotenoids once the sweet corn genotypes overcame initial herbicidal photo-oxidative stress. This is the first report of herbicides directly up regulating a key biochemical pathway linked to the nutritional quality of a vegetable crop.