Salt-tolerant maize (STM) and salt-sensitive maize (SSM) were treated with 100 mM NaCl for 1, 3 and 6 d and the contents of Na+ and Cl(-) (cps) of different organelles of leaf cells determined by X-ray microanalysis. The results showed that Na+ and Cl(-) entered the cytoplasm, vacuole, chloroplast and apoplast simultaneously. When STM and SSM were treated in 100 mM NaCl at atmospheric pressure (-P) and with pressure equivalent to the osmotic pressure of the NaCl (+P), the dry weights of STM (+P) and SSM (+P) plants were greater than that of STM (-P) and SSM (-P) plants, showing that the inhibitory effect of salt on plant growth was at least partially due to the osmotic effect of the NaCl. When STM and SSM were treated with NaCl and iso-osmotic polyethlene glycol, the dry weights of plants given the iso-osmotic polyethlene glycol treatment were lower for both maize lines than that of the NaCl-treated plants. Our data show that under NaCl stress, both STM and SSM seedlings simultaneously suffered from osmotic and ion stresses.

According to a survey conducted from 1995 to 2004 in the eight regions with salinized soils, China contains 587 halophytes representing 242 genera and 71 families: apart from three species of ferns, all are angiosperms. Physiologically, Chinese halophytes include salt-secreting halophytes, euhalophytes, and pseudohalophytes. Ecologically, Chinese halophytes include zerohalophytes, mesohalophytes, and hydrohalophytes. Chinese halophytes represent a salt-tolerant gene pool that might be used to increase the salt tolerance of conventional crops through breeding, but also have considerable potential as salt-tolerant economic crops providing food, forage, medicine, and industrial material in salinized soils.

The authors found five sodium (Na + ) and chloride (Cl − ) hyperaccumulating halophytes in the Temperate Desert of Xinjiang, China and studied two of them (Suaeda salsa (L.) Pall. and Kalidium folium (Pall.) Moq.). K. folium and S. salsa had a NaCl content of 32.1% and 29.8%, respectively, on a dry weight basis. X-ray microanalysis of the Na + in the vacuole, apoplasts and cytoplasm of the two plants indicated a ratio of 7.3:5.6:1.0 in K. folium and 7.3:6.6:1.0 in S. salsa. These data show that K. folium and S. salsa both have a high Na + and Cl − accumulating capacity, which is related to high activity of tonoplast H + -ATPase and H + -PPase. (Pall.) Moq.; Na + ; Suaeda salsa (L.) Pall.; vacuole.During the investigation of halophytes in Xinjiang in 2000 and 2001, we found some members of the Chenopodiaceae in the salt desert and salt marshes that were hyperaccumulators of sodium (Na + ) and chloride (Cl − ). The plants included Halocnemum strobilaceum (Pall.) Bieb., Halostachys caspica (Bich.) C. A. Mey, Kalidium folium (Pall.) Moq., Suaeda salsa (L.) Pall. and Salicornia europaea L. (Zhao and Li 1999), all of which retain high quantities of Na + and Cl − (amounting to 26.9%-30.5% of their dry weight), especially in the shoots. The salt content of these plants is 150-180-fold higher than in glycophytes and is also 4-6-fold higher than in other halophytes such as Lyceum ruthenium Murr. and Korelinia caspica (Pall.) Less. (Hou 1982). Some hyperaccumulators, such as Silene aprica L. and Pteris vittata L. which can accumulate copper (Cu) to 1.3% and arsenic (As) to 0.32%-0.49%, respectively, can reduce soil contamination (Hou 1993;Lena et al. 2001;Xe 2001), thus serving as a phytoremediation strategy (Mckensie and Leshen 1994).It is hoped that Na + and Cl − hyperaccumulators can be used for the desalination of soils, because this biological strategy is economical and without side effects (Zhao et al. 2001). We selected two hyperaccumulators, K. folium, a native species of the salt deserts and Suaeda salsa, a native of salt marshes, to study the mechanisms of Na + and Cl -hyperaccumulation.

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