This is the review of the studies on the structure of ion exchange membranes prepared by thepaste method. The ion exchange membranes are practically used in various ways. Since the pastemethod has been invented in 1960, the membranes have been improved to enhance their properties. Then the understanding of the membrane structure has been necessary to support the improvementof the membranes. Accordingly, the membrane structure has been studied so far by using variousmethods. Now, it is elucidated that the membranes contain a microheterogeneity in a colloidalorder, an interpenetrating polymer network in other words. This is the keypoint to make it possible to prepare the excellent ion exchange membranes with the well-balanced properties.
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 SO42- 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.
Six species of mangrove plants used for this study are of those which can adjust the absorptionof ions in the root-cell membranes for their normal growth. In the roots (root hairs and mainroots) of these used mangrove plants, Na ion and Cl ion were accumulated remarkably with suchhigh concentration that could never be recognized in upland plants except those plants grown inthe saline-soil area. For the normal growth of many other ordinary plants, in general, toxic ions are first accumulatedin their roots. In the case of these used mangrove plants, the study suggested that the excessivelyabsorbed Na ion and Cl ion be first accumulated in their roots, but then transported to theirstems through the vessels to be accumulated in their leaves and finally discharged from the saltglands of their leaves or discarded with fallen leaves. On the other hand, K ion for the normal growth of plants was found in the analyzed mangroveplants, and the amount of its concentration was different from each other according to the species.The Na/K ratio of the analyzed mangrove plants was (8-27):1, and the ratio suggested that K ionwas absorbed selectively and actively from sea water (Na/K ratio of sea water 47:1). Organic acids in the analyzed mangrove plants were oxalic acid as a main and malic acid, and they were spent for the neutralization of the excessively absorbed cations for the normal growth.