Abstract: In order to study the effects of salt stress on proline accumulation and the activities of the key enzymes involved in proline metabolism a pot experiment was conducted using wild Medicago ruthenica stressed under different NaCl and Na₂CO₃ solutions; 0, 50, 100, 200, 300, 400 and 500 mmol·L^-1. The result showed that, under salt stress, proline content and P5CS and δ-OAT activity gradually increased while ProDH activity declined with increasing salt concentration. The initial accumulation of proline was a major reason for the reduced damage from NaCl and Na₂CO₃ stress in M. ruthenica seedlings. The Glu and Orn pathways were synergistic to the accumulation of proline, with the Orn pathway playing a leading role. This study suggests that the concentration of NaCl and Na₂CO₃ should not exceed 400 mmol·L^-1 for M. ruthenica.

Key words: Medicago ruthenica, salt stress, proline, pyrroline-5-carboxylate synthetase, ornithine-oxo-acid transaminase, proline dehydrogenase