Weedkiller ups nutrients.(Plant science)

A new study indicates herbicides can increase the nutrients in crops, adding a new dimension to the debate on agrochemical use.

The researchers applied two common herbicides, mesotrione and atrazine, to several varieties of corn. After 45 days, they found that mature kernels from treated plants had up to 15% more carotenoids, including lutein and zeaxanthin, than the unsprayed plants (J Agric Food Chem doi:10.1021/jf9013313).

Carotenoids are pigments used in photosynthesis, which have antioxidant properties thought to confer health benefits. Many experts think lutein and zeaxanthin could help prevent agerelated macular degeneration (AMD), an eye disease that affects almost 2m people in the US.

Mesotrione kills plants by preventing the synthesis of carotenoids. But some varieties of corn are resistant to the chemical. According to co-author Dean Kopsell, a crop physiology professor at the University of Tennessee, US, the initial stress is important.

'During this stress, a key precursor for carotenoid synthesis was accumulating, since the pathway was blocked by the active chemical,' he says. 'Once the plants out-grew the symptoms, re-greened, and set the ears, this precursor was free to enter into carotenoid synthesis again, which resulted in greater carotenoid pools in the kernels.'

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The effect is unlikely to immediately benefit farmers. 'The money farmers receive makes up only a small portion of the prices people pay,' Kopsell says. 'Thus, farmers are paid mostly on how much they can produce. Until the system changes, and farmers start getting paid based on nutritional quality aspects, I don't see this idea creating much in terms of profits.'

But, in the meantime, the effect could be recreated with other combinations of herbicides and food crops. The group is testing onions and chives, which are in the same family as corn.

'Observational studies have shown that dietary intake of carotenoids is associated with a reduced risk of some types of cancer, including lung and stomach cancer,' says Claire Williamson, a nutrition scientist at the British Nutrition Foundation. 'However, the results of intervention studies using supplements have failed to back up these findings. It is therefore likely that there is a complex interaction between the many components found in plant foods and the rest of the diet.'

'There is increasing interest in whether carotenoids can reduce AMD,' she continues. 'A high level of carotenoids may protect the retina by limiting oxidative stress that results from metabolic processes.'

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