Air Date: Week of October 12, 2001

A preliminary study shows that synthetic chemicals that mimic estrogen may be interfering with a vital plant process. Living on Earth's Diane Toomey reports.

Transcript

CURWOOD: Nitrogen is one of the building blocks of life, and, while there is plenty of it in the air, it's not in a form that plants and animals can use. But bacteria can convert nitrogen into plant food, through a process called nitrogen fixing. A study published recently in the journal Nature offers preliminary evidence that synthetic chemicals that mimic estrogen might be affecting this process. If true, both agricultural and wild plant systems could be at risk of disruption. Living on Earth's Diane Toomey reports.

TOOMEY: Members of the plant family known as legumes range from dwarf herbs in the Arctic to massive trees found in tropical forests, and they include cultivated crops like alfalfa and soy beans. To thrive in nitrogen-poor soils these plants have developed a survival strategy: they produce a natural form of estrogen that attracts soil bacteria into their roots, where these microorganisms begin the process of nitrogen fixation. This produces fertilizer for the plants and a form of nitrogen that's distributed throughout the food chain when these plants are eaten.

Since a natural estrogen kicks off this process, researchers at Tulane University wondered-

McLACHLAN: Could chemicals block the effect of the natural stimulator.

TOOMEY: John McLachlan directs Tulane University's Center for Bio Environmental Research. He says since manmade chemicals can disrupt hormonal systems in animals, they might be doing the same thing in certain plants. So he and colleagues grew bacteria and alfalfa together in petri dishes, then added certain pesticides and other chemicals that are known estrogen mimickers. They also added something called a reporter gene into the mix. This gene produces a blue color when the bacteria receive an estrogen signal.

McLACHLAN: In a root tip that is trying to accumulate some of these bacteria, in the presence of one of the synthetic chemicals would actually block the activation of the bacteria such that you can't see any color at all. Even though the bacteria themselves are there, they're not participating in this sort of chemical exchange or chemical dance that's occurring.

TOOMEY: In other words, the bacteria never got the signal to enter the root and begin converting nitrogen. Although these synthetic chemicals are widely distributed throughout the environment, Professor McLaughlin says so far, no one has looked for this disruption anywhere beyond a petri dish. And, out of the 100 or so chemicals tested in his lab only a handful actually blocked the plant estrogen. But he says nature uses many signaling systems of the type studied here.

McLACHLAN: It's only now that we're even starting to look at the way the synthetic chemical environment might affect these global networks of signals.

TOOMEY: So, Professor McLaughlin says, this small observation should be used as a starting point for further research, especially since the legume family of plants that depend on estrogen signaling for their survival are key to agriculture and make up a significant portion of many ecosystems. For Living on Earth, I'm Diane Toomey.