Abstract:

Exogenous nitric oxide (NO) releaser sodium nitroprusside (SNP) with different concentrations from 0.01 to 5.00 mmol/L induced proline accumulation in wheat (Triticum aestivum L. cv. Yangmai 158) seedling leaves under 150 mmol/L salt stress in a dose-dependent manner. It was most effective at 0.1 mmol/L SNP, and the combination treatments with two NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) and hemoglobin, separately reverted the 0.1 mmol/L SNP induced proline accumulation. Meanwhile, the proline accumulation induced by NO might be of benefit to the water retention in wheat seedling leaves when subjected to salinity, and exogenous 0.1 mmol/L SNP treatment also dramatically activated the synthesis of endogenous abscisic acid (ABA), and the employment of hemoglobin further indicated that NO might be downstream of the ABA induced proline accumulation in wheat seedling leaves under 150 mmol/L salt stress, but there did not exist synergism between NO and ABA signaling toward proline accumulation. Detection of proline synthesis and degradation demonstrated that exogenous NO induced proline accumulation in a phase dependent manner, mainly by enhancing the activities of D¹-pyrroline-5-carboxylate synthetase (P5CS) within the first 4 d of treatment and inhibiting activities of proline dehydrogenase (ProDH) 4 d later up to 8 d. And ABA showed a weak effect on P5CS and ProDH activities in comparison with NO treatment. Additionally, Ca²⁺ was confirmed as the important intermediates during the NO signaling pathway in proline accumulation under salinity conditions.

Key words: wheat (Triticum aestivum), nitric oxide (NO), abscisic acid (ABA), proline, salt stress