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Studies on Mechanism of Salt Tolerance of Zoysia spp.
In Taiwan, Zoysia spp. from different ecotopes significantlly varied in the ability of salt tolerance. The clones of Zoysia spp. with higher salt tolerance could survive in the solution with 7.5% NaCl, about 2.5 times of sea water concentration. Those with lower salt tolerance could also tolerate with the salinity about half to equal concentration of sea water. Thus Zoysia spp. could be defined as halophytes. Under highly saline environment, Zoysia spp. not only challenged to the ionic toxicities, but also adapted to the osmotic stress which was caused by the high concentration of salt ions. Zoysia spp. owned both morphological and physiological characters of draught tolerance for adapting to the osmotic stress. In the view of morphological features, stomata on the adaxial epidermis were surrounded by several ball- shape structures and subsided. In some clones, stomata on abaxial epidermis were more than that on the adaxial epidermis. The abaxial epidermis was not covered with wax, while the adaxial epidermis was covered with wax. The stomata of some clones were covered with wax. These structural characteristics could help reduce water loss and increase drought tolerance. In the view of physio- logical features, Zoysia spp. could accumulate solutes to lower osmotic potential and maintain turgor pressure in the cell through osmotic adjustment to reduce the damages. The accumulated solutes consisted of the out-coming inorganic ion such as Na+, and the synthesized products such as soluble sugar and proline. Among the total solutes, the Na+ played the most important role to osmotic adjustment among the solutes. For adapting ionic toxicities, Zoysia spp. could extrude salt by the salt glands which were located on the adaxial epidermis to reduce the salt accumulation and damages. The clones of Zoysia spp. with higher salt tolerance had much more salt glands on the adaxial epidermis and were more active in salt-excreting than those with lower salt tolerance. Further, the membrane system of Zoysia spp. with higher salt tolerance was more stable to maintain the regular selective permeability to prevent the cell from leaking under high concentration of Na+ accumulated.
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