In situ and in vitro binding of natriuretic peptide hormones in Tradescantia multiflora

An increasing body of evidence suggests that in plants, as in vertebrates, biologically active natriuretic peptide (NP) hormones play an important rol e in the regulation of the osmotic and ionic balance. The evidence includes isolation and immunoaffinity purification of biologically active natriuret ic peptide analogues (irPNP) from ivy that promoted stomatal opening and sp ecifically, rapidly and transiently increased cGMP levels in root conductiv e tissue. In this study we demonstrate that I-125-rat atrial natriuretic pe ptide (rANP) binds to plasma membranes from leaf and stem tissue of Tradesc antia multiflora and importantly, both unlabelled rANP and irPNP can compet itively displace that binding. In addition, tissue section autoradiography reveals specific in situ binding of I-125-rANP to leaf and stem tissue. The findings are consistent with the presence of a biologically active NP syst em in plants and suggest that NPs signal through a dedicated receptor syste m.