Helping Crops Shed Pesticides

5 October 2009 (All day)

George Doyle/Stockbyte

Self-help. Spraying crops with a common plant hormone boosts their ability to purge pesticide residues.

Every year, 3 million tons of pesticides are sprayed on the world's food crops. The chemicals protect plants from voracious insects and pathogens, and they save billions of dollars in damages. Yet high doses of pesticides that accumulate in the body can cause cancer and other serious illnesses in humans--a problem that is widespread in the developing world and until now has remained largely unresolved. Now scientists may have found a way to help crops shed these toxicants long before they end up on dinner tables around the globe.

The idea involves dousing agricultural crops with a naturally occurring plant hormone that seems to boost the ability of the plants to remove pesticide residue in their cells. Agronomist Jing-Quan Yu and colleagues from Zhejiang University in Hangzhou, China, focused specifically on a group of hormones called brassinosteroids. The compounds, which Yu says are ubiquitous, help plants cope with extreme temperatures, drought, and even invasive microbes. Yu and his colleagues wanted to see whether brassinosteroids could fight off pesticides as well.

Starting in 2006, Yu's team tested the effect of brassinosteroids on young cucumbers, tomatoes, Chinese cabbage, and tea plants. The researchers sprayed the plants with a solution of water and hormone concentrate up to 3 days before the application of pesticides. As the team reports in the current issue of the Journal of Agricultural and Food Chemistry, the brassinosteroids reduced the pesticide-residue content inside the plants by as much as 70%. The treatment does not affect the ability of pesticide residue on the outside of the plants to thwart invaders.

Yu's team found that brassinosteroids work by activating cellular processes that help the plants expel the pesticides from their cells more effectively. When the team laboratory-tested a substance that inhibits the absorption of brassinosteroids by the plants, the reduction in pesticide residues was reversed. "We were quite excited by our findings," says Yu. "I could not sleep the [first] night when we obtained the data."

Yu says the hormones, which have "a very low toxicity," can be developed for commercial use either by spray application or by genetically altering the plants to boost their production of the hormones.

It's a "novel" study with valuable implications, says environmental chemist Jay Gan of the University of California, Riverside. But further research is needed, he says, to see if brassinosteroid treatments can also reduce pesticide residues in mature, edible plants. Nevertheless, Gan adds, because poisoning from pesticide residues on leafy vegetables and fruits is a serious human health concern, especially in developing countries, the study should lead to a new line of research to minimize the residues in fresh produce.