Effects of NaCl Stress on Proline Accumulation and Metabolic Pathways of Chicory(Cichorium intybus L.) Seedlings

Proline plays important roles in regulation of osmotic homeostasis,prevention of damages caused by osmotic stresses,scavenging of reactive oxygen species and protection of cell structures.Many plants accumulate proline dramatically under a variety of stress conditions.The regulation of proline accumulation in Chicory seedlings and the activities of key enzymes involved in proline metabolism in response to salinity were studied here.Fifty-day-old seedlings were treated with NaCl(0,100,200,300 and 400 mM) in this experiment.Results show that Ornithine-oxo-acid transaminase(δ-OAT) activity increases;Pyrroline-5-carboxylate synthetase(P5CS) activity initially increases then deccreases,while ProDH activity decreases with increasing NaCl concentration.Proline contents increase significantly(P0.05) with increasing salt-stress followed by a declining response during the extending salt-stress period.The data demonstrate that glutamate and ornthine pathways are activated by NaCl.The glutamate pathway is predominant under low-concentration NaCl treatments,and an ornithine pathway is predominant under high-concentration NaCl treatments.