The coordinated alterations in antioxidative enzymes, PeCu/ZnSOD and PeAPX2 expression facilitated in vitro Populus euphratica resistance to salinity stress

Populus euphratica Oliv. response to salinity stress has been mainly studied at a whole-plant level. However, many genes associated with salinity tolerance are constitutively expressed or show strong organ-or tissue-specific, and the relationship between reactive oxygen species (ROS) and the antioxidant system has been rarely investigated. In present work, the effects of salinity treatments (0, 50, 100, 150, and 200 mM NaCl) on cell ultrastructure, ROS, antioxidant enzymes, and relevant gene expressions were investigated to get an overview of salinity stress response of P. euphratica micro-shoots under in vitro conditions. Antioxidant enzymes such as superoxide dismutase (SOD) and ascorbate peroxidase (APX), etc., were activated in the presence of low and moderate salt stress (≤ 150 mM NaCl). Regulation of ROS levels and the cellular redox equilibrium, as well as an increase in glutathione (GSH) and ascorbic acid (AsA) content, were also recorded at 150 mM NaCl. PeCu / ZnSOD upregulation occurred 12 h before PeAPX2 upregulation at 100 mM NaCl. The enzymes SOD, APX, CAT, and POD were inhibited by high salinity stress (200 mM NaCl), whereas the level of H 2 O 2 was significantly increased. PeCu / ZnSOD expression increased after 12 h, whereas PeAPX2 expression increased after 36–72 h at 200 mM NaCl. This resulted in a burst of O 2 .− and H 2 O 2 , which accelerated membrane lipid peroxidation, significantly reduced chlorophyll content, and eventually led to chlorosis and cellular damage. In this study, the bigger contributing markers to salt tolerance were AsA, APX, CAT, and SOD. Our results indicated the coordinated alterations between enzymatic, ROS and gene expressions facilitated the resistance to salinity in P. euphratica micro-shoots under moderate salinity.