Differential estrogenic activities of male and female plant extracts from two dioecious species

Abstract

The reconstituted steroid transcription unit in Saccharomyces cerevisiae transformed with both a human estrogen receptor expression plasmid (YEPE10) and a reporter plasmid (YRPE2) was used to screen for estrogen compounds in cell extracts prepared from female and male plants of osage-orange, Maclura pomifera (Raf.) Scheind. and mulberry, Morus microphylla Buckl. ( Moraceae). Phytoestrogens in the plant extracts induced the transcription of the reporter gene in transgenic yeast. The transcriptional activity increased proportionally with increased amounts of plant extracts added to the yeast cells. Female mulberry and osage-orange plant extracts activated transcription of the steroid reporter gene about 15 times and 4 times, respectively, compared to the corresponding male plant extracts. The putative phytoestrogen from Maclura was lipid soluble, and co-migrated with sterols (17 β-estradiol) and isoflavones (genistein) in TLC separations. The active fractions recovered from TLC plates exhibited UV-absorption spectra similar to authentic estradiol and genistein. The putative phytoestrogen appeared to be synthesized at specific developmental stages in female Maclura plants; levels of transcriptional activity were higher at times prior to and during flowering (February–April). Moreover, extracts from monoecious members of Moraceae, Ficus species (fig and rubber tree) did not activate transcription of the steroid reporter gene in the yeast system. Collectively, these data correlate the occurrence and levels of endogenous phytoestrogens with female individuals of two dioecious species, suggesting a possible pattern or strategy in the reproductive ecology of these dioecious species.