Effect of salt on ROS homeostasis, lipid peroxidation and antioxidant mechanisms in Pinus pinaster suspension cells

In the Pinus genus, information on the effectiveness of oxidative defence mechanisms during exposure to salt is lacking. The effect of salt stress imposition on ROS homeostasis was investigated using maritime pine (Pinus pinaster Ait.) suspension cells as a model system. Cells were maintained in MS-based medium, exposed to salt (50, 100 and 150 mM NaCl) and analysed for biomass production, evidencing a decreasing growth capacity. Use of 100 mM NaCl imposed severe salt stress without affecting cell viability, being chosen for subsequent studies on the ROS homeostasis of salt shock-treated suspension cells. Increased total ROS levels were evident on the second day of salt exposure, but a superoxide ion transient burst was immediately noticeable. Additionally, lipid peroxide formation seemed to correlate with superoxide ion breakdown. In-gel superoxide dismutase activity evidenced a FeSOD homodimer with strongly increasing activity between hours 12-48 of salt stress imposition. Subsequently, P. pinaster Fe-Sod1 and csApx1 genes were isolated from a cDNA library and expression was shown to increase within 12-24 h. Results show that severe salt treatment generates oxidative stress in P. pinaster cells despite the induction of antioxidant systems, and suggest a putative involvement of ROS in salt stress signalling.