Soil salinization has become one of the resource and ecological problems all over the world, and it is one of the important abiotic stress factors that affect crop production. In order to fully develop the saline soil resources and saline soil agriculture, the selection and breeding of salt-tolerant plants with economic values has been attracting more and more attention. Salt-tolerant plants have evolved into complicated salt-tolerant mechanisms which enable them to thrive in high-salt environments and they can be either domesticated into new salt-tolerant crops or used as a potent genetic source for improving the salt tolerance of conventional crops through genetic engineering methodology. So it is very important to study the salt-tolerant physiological mechanisms and determine the key genes of salt tolerance for breeding the new salt-tolerant species by use of genetic engineering, which is of extremely important theoretical and practical significance for the sustainable development of saline soil amelioration and saline agriculture. This work firstly studied the physiological response of Kosteletzkya virginica to salt stress and proline accumulation was found in the leaf of seedlings under salt stress. To explore the cause behind proline accumulation , we first cloned proline metabolism-related genes and investigated their expression and function. The main results are as follows:
  (1) After treatment by different concentrations of NaCl for 20 days, the growth parameters of Kosteletzkya virginica seedlings were almostly unaffected under 100 and 200 mmol/L NaCl stress. Although Na⁺ content in the leaves and roots was significantly increased, more Na⁺ was compartmented into roots and the leaves had higher K⁺/Na⁺ ratio and higher proline content than roots, indicating that both inorganic ions and organic solutes of seedlings were involved in the osmotic adjustment to counter salt stress. Compared with the control, no significant difference was found in chlorophyll fluorescence parameters, MDA content and cell membrane permeability. Maybe the increased activitiy of antioxidant enzymes protected the seedlings from oxidative damage caused by reactive oxygen species. Under 300 and