Proline metabolism in response to salt stress in common reed [Phragmites australis (Cav.) Trin. ex Steud

Abstract

Abstract We studied effects of salt stress on proline accumulation and the activities of proline metabolic enzymes in reed, a salt-tolerant, cosmopolitan, aquatic grass. A concentration-dependent inhibition of plant growth occurred in the presence of NaCl, which was accompanied by high amounts of proline accumulation. Reed tolerance of salt stress reaches a limit at approximately 200 mm NaCl. Free proline content and pyrroline-5-carboxylate synthetase (P5CS) activity both increased with salt stress treatment, while ornithine aminotransferase (OAT) activity appeared to be unaffected, suggesting that the glutamate pathway, rather than the ornithine pathway, plays a vital role in proline accumulation during osmotic regulation. The activity of the proline degrading enzyme, proline dehydrogenase (PDH), decreased under salt stress, indicating that proline catabolism may also be responsible for proline accumulation in response to salt stress. Furthermore, high salinity ≥250 mm NaCl, which stops growth of reed, decreases proline accumulation and P5CS, OAT, and PDH activities. This suggests that changes in enzyme activities of proline metabolism coupled with increased proline accumulation are involved in osmotic regulation of reed plants only when they are grown at salinities ≤200 mm NaCl.