09/07/09 Scientists are reporting for the first time that the use of weed killers in farmers' fields boosts the nutritional value of an important food a crop. Application of two common herbicides to several varieties of sweet corn significantly increased the amount of key nutrients termed carotenoids in the corn kernels, according to a study scheduled for publication in the July 22 issue of ACS' Journal of Agricultural and Food Chemistry, a bi-weekly publication.

In the new study, Dean Kopsell and colleagues note that farmers grow about 240,000 acres of sweet corn in the United States each year, making it an important food crop. Corn is among only a few vegetable crops that are good sources of zeaxanthin carotenoids. Consuming carotenoid-rich vegetables may reduce the risk of age-related macular degeneration (a leading cause of vision loss among older people), heart disease, and cancer, the study notes.

The scientists exposed several varieties of sweet corn plants to the herbicide mesotrione or a combination of mesotrione and atrazine, another commonly used weed killer, and harvested mature corn 45 days later. Herbicide applications made the corn an even-better source of carotenoids, boosting levels in the mature kernels of some varieties by up to 15 percent. It specifically increased levels of lutein and zeaxanthin, the major carotenoids in sweet corn kernels, which studies have linked to a reduced risk of age-related macular degeneration.

According to the authors, the herbicide mesotrione inhibits a critical enzyme, phytoene desaturase, in plant carotenoid biosynthesis. Mesotrione is currently labeled for selective weed control in sweet corn (Zea mays var. rugosa). Mesotrione applied alone, or in mixtures with the photosystem II inhibitor atrazine, acted to increase concentrations of kernel antheraxanthin, lutein, and zeaxanthin carotenoids in several sweet corn genotypes. Kernel lutein and zeaxanthin levels significantly increased 15.6% after mesotrione + atrazine early postemergence applications, as compared to the control treatment. It appears that mesotrione applications resulted in greater pools of kernel carotenoids once the sweet corn genotypes expressing moderate injury overcame the initial herbicidal photo-oxidative stress. This is the first report of herbicides directly up-regulating the carotenoid biosynthetic pathway in corn kernels, which is associated with the nutritional quality of sweet corn. Enhanced accumulation of lutein and zeaxanthin is important because dietary carotenoids function in suppressing aging eye diseases such as macular degeneration, now affecting 1.75 million older Americans.