Atrial natriuretic-like peptide and its prohormone within Metasequoia

Metasequoia glyptostroboides was one of the dominant conifers in North Amer ica, Asia, and Europe for more than 100 million years since the late Cretac eous Albian Age, but Quaternary glaciations drove the Metasequoia populatio n to apparent extinction. A small pocket of Metasequoia, however, was found in central China in the 1940s representing the only surviving population o f this "living fossil" species. Atrial natriuretic peptide, a 28-amino-acid peptide hormone that causes sodium and water excretion in animals, has bee n found to be part of the first peptide hormonal system in lower plants. Th e existence of this hormonal system has never been examined within trees of any genus. High-performance gel permeation chromatography of the leaves an d stems (i.e., branches) of Metasequoia followed by atrial natriuretic pept ide radioimmunoassay revealed an ANP-like peptide and its prohormone (i.e., approximate to 13,000 mot wt) were present in both leaves and stems of thi s conifer. The elution profile of ANP-like peptide in stems of Metasequoia had a shoulder to the left of where pure synthetic ANP elutes suggesting th e possibility of a slightly larger peptide eluting within this shoulder sec ondary to alternate processing of the ANP-like prohormone and similar to wh at occurs with the kidney of animals. The elution profile of ANP-like pepti de in the leaves of Metasequoia revealed two peaks; one where ANP elutes an d a second peak suggesting a smaller peptide that has been metabolically pr ocessed. The presence of the ANP-like prohormone strongly suggests that ANP -like gene expression is occurring in both leaves and stems of Metasequoia since this prohormone is the gene product of this hormonal system. The pres ence of the ANP-like hormonal system in trees implies that this hormonal sy stem may have been present early in land plant evolution to allow trees to reach heights of greater than 30 feet where a water flow-enhancing substanc e is absolutely necessary for water flow to occur to these heights.