Presence of estrogens and estrogen receptor-like proteins in solanum glaucophyllum

The synthesis of mammalian steroid hormones by plants has been reported. However, their physiological role in plants is controversial. The existence of receptor molecules as those of animal cells could provide clues into a possible steroid mechanism of action. Solanum glaucophyllum callus cultures were found to contain not only 17β-estradiol and estrone but also abundant estrogen binding sites. These sites were specific for 17β-estradiol (∼550 fmol/mg protein) and could also be competed by the known estrogen receptor (ER) agonist diethylstilbestrol. Antibodies directed against specific sequences of the classical ER α isoform, labelled a ∼67 kDa band which comigrated with the mammalian ER α antigen. ER α-like proteins were tested positive as estrogen binders in Ligand blot experiments using 17β-estradiol macromolecular derivatives as ligands. Our results provide first evidences on the existence of estrogen binding proteins structurally related to the mammalian ER α subtype in a higher plant system.