Abstract
Mangrove plants are distributed along coastal areas and estuarine areas of the sub-tropical and tropical worlds which include Okinawa, Japan. These are called halophytes which possess peculiar physiological mechanisms for salt control. Characteristic distribution of mangrove plants is observed as conditioned by tidal regime and salinity.
Bruguiera gymnorrhiza (Japanese name: Ohirugi) is one of the mangrove species and its distribution in a mangrove forest is confined to the areas that are not strongly affected by sea water. In this study, Bruguiera gymnorrhiza was compared under different NaCl conditions of culture solution. The inorganic ions (anions and cations) and organic acids in leaves, rhizophores and roots parts in each cultured sample were analyzed, respectively. Bruguiera gymnorrhiza grew very well under F-20 culture condition (0.6% NaCl) like a natural growth in the mangrove forest. Leaf size was large and leaf color also was a healthy green. On the contrary, at high salinity condition (F-100, 3% NaCl) the leaf of Bruguiera gymnorrhiza was small and thick. These thick leaves contained high amount of Na+ and Cl- ions. After culturing, ion components of culture solution were also analyzed. The data indicated that K+, PO43-, and NO3- ions in culture solution were decreased or disappeared by absorption for plant growth. These three elements are essential elements for plant growth. Na+, and Cl- ions were also absorbed and translocated to upper parts, then these ions were stored in the leaves. Furthermore, leaves gradually increase succulences and finally these leaves will fall down because of NaCl abandonment from plant body. Production of organic acids depends on salinity condition. All leaves, rhizophores and roots contained high amount of oxalic and malic acids. These dicarboxylic acids are important for osmotic regulation of halophytes.
