Abstract
We studied salt homeostasis in mangrove. Ion contents were measured in various organs of several mangrove species distributed in Iriomote Island, resulting that seawater-derived sodium was detected in every vegetative organ of shoots. Sodium content of propagules was however significantly lower than that of other vegetative organs in all the species assayed suggesting a sodium filtration between these organs. Concentration gradient of sodium between propagules and other organs was highest in Avicennia marina. Moreover as Na+/K+ ratio was lower than 1 only in A. marina, this species was expected to selectively filtrate sodium. We hypothesize that xylem sap needs to pass through the parenchyma for the selective ionic filtration. A placenta to which vascular bundles from a flower stalk connected adjoined a hypocotyle at each parenchyma. Further analysis using a fluorescent sodium indicator showed organ-specific localization of sodium, concluding that A. marina filtrated sodium selectively and effectively in placenta cells.
