Study on Salt Excretion from Salt Glands of Ancennia marina

Abstract

Avicennia marina is one of mangrove plants and has salt glands on leaf surfaces for osmoticcontrol by salt excretion. This Avicennia marina distributes and grows in the most front areas ofthe mangrove forests in the sub-tropical and tropical zones of the world. And, this species isusually influenced by the tidal condition of sea water.
White precipitated, crystallized substances on leaves were mostly pure sodium chloride (NaCl). Excretion components of inorganic ions from salt glands of leaves were Na⁺ and Cl^- as main excretedions, and the excretion amount of these ions increased with the rise of NaC1 concentrationin cultural solution. K⁺, Mg²⁺, Ca²⁺ and SO₄^2- were also detected in rinsed water of sample leaves.
Amount of distributed Na+ and Cl^- in the leaf and the root increased with the rise of NaCl concentrationin cultural solution. Amount of distributed Na⁺ and Cl^- in the leaves was higher thanthat in the roots. It was suggested that these ions passed through root cell membranes wererapidly transported into the leaves through the vessel tissue. And water transported to the leaveswas concentrated by transpiration from leaf surface, and the concentration of inorganic ions in thewater-storage tissue of the leaves increased.
Relationship between the amount of organic acids in the leaf and the root and NaCl concentrationin cultural solution can not be definitively discussed at present. But, the excessively absorbedinorganic ions (Na⁺ and Cl^-) in the leaves are considerably excreted from the salt glands of leafsurfaces, and controlled or balanced with the salt concentration in the leaf tissues for osmotic pressurecontrol.
Other many halophytes we used for the neutralization pathway of excessively absorbed cationswith organic acids (salt as derivative) for osmotic pressure control in plant cells. This study suggeststhat the mechanism of the neutralization pathway of excessive cations for osmosis regulation in the leaf cells and the root cells is not so important in the Avicennia marina.