Nitrogen fixation. Endocrine disrupters and flavonoid signalling.

Nitrogen fixation is a symbiotic process initiated by chemical signals from legumes that are recognized by soil bacteria. Here we show that some endocrine-disrupting chemicals (EDCs), so called because of their effect on hormone-signalling pathways in animal cells, also interfere with the symbiotic signalling that leads to nitrogen fixation. Our results raise the possibility that these phytochemically activated pathways may have features in common with hormonal signalling in vertebrates, thereby extending the biological and ecological impact of EDCs.

The inhibition of estrogen receptor-mediated responses by chloro-S-triazine-derived compounds is dependent on estradiol concentration in yeast.

The chloro-S-triazine derived compounds atrazine, atrazine desisopropyl, cyanazine, and simazine are commonly used herbicides. These compounds do not have estrogenic activity in yeast expressing human estrogen receptor (hER) and an estrogen-sensitive reporter. In the presence of a concentration of estradiol (20 nM) that induced maximal reporter activity in yeast, the triazines did not inhibit reporter activity. However, the triazines decreased reporter activity in a dose dependent manner in the presence of a submaximal concentration of estradiol (0.5 nM). The estradiol-dependent activity of a mutant hER lacking the amino terminus was not inhibited by the triazines in yeast. Competition binding assays demonstrated that the triazines displaced radiolabeled estradiol from recombinant hER. These results suggest that the ability of the triazines to inhibit estrogen receptor-mediated responses in yeast occur through their interaction with hER and is dependent on the concentration of estradiol.