Heme Oxygenase-1 is Associated with Wheat Salinity Acclimation by Modulating Reactive Oxygen Species Homeostasis

Heme oxygenase-1 （HO-1） has been recently identified as an endogenous signaling system in animals. In this study, HO-1 upregulation and its role in acquired salt tolerance （salinity acclimation） were investigated in wheat plants. We discovered that pretreatment with a low concentration of NaCl （25 mmol/L） not only led to the induction of HO-1 protein and gene expression, as well as enhanced HO activity, but also to a salinity acclimatory response thereafter. The effect is specific for HO-1, since the potent HO-1 inhibitor zinc protoporphyrin IX blocks the above cytoprotective actions, and the cytotoxic responses conferred by 200 mmol/L NaCl are reversed partially when HO-1 inducer hemin is added. Heme oxygenase catalytic product, carbon monoxide （CO） aqueous solution pretreatment, mimicked the salinity acclimatory responses. Meanwhile, the CO-triggered re-establishment of reactive oxygen species （ROS） homeostasis was mainly guaranteed by the induction of total and isozymatic activities, or corresponding transcripts of superoxide dismutase, ascorbate peroxidase, and cytosolic peroxidase （POD）, as well as the downregulation of NADPH oxidase expression and cell-wall POD activity. A requirement of hydrogen peroxide homeostasis for HO-1-mediated salinity acclimation was also discovered. Taken together, the above results suggest that the upregulation of HO-1 expression was responsible for the observed salinity acclimation through the regulation of ROS homeostasis.

Changes in Plasma Osmolality, Cortisol and Amino Acid Levels of Tongue Sole(Cynoglossus semilaevis) at Different Salinities

A serial of salinity transferring treatments were performed to investigate the osmoregulation of tongue sole(Cynoglossus semilaevis). Juvenile tongue sole were directly transferred from a salinity of 30 to 0, 10, 20, 30, 40 and 50. Blood sampling was performed for each treatment after 0, 1, 6 and 12 h, as well as after 1, 2, 4, 8, 16 and 32 d. The plasma osmolality, cortisol and free amino acids were assessed. Under the experimental conditions, no fish died after acute salinity transfer. The plasma cortisol level increased 1 h after the abrupt transfer from a salinity of 30 to that of 0, 40 and 50, and decreased from 6 h to 8 d after transfer. Similar trends were observed in the changes of plasma osmolality. The plasma free amino acids concentration showed a ‘U-shaped' relationship with salinity after being transferred to different salinities for 4 days. More obvious changes of plasma free amino acid concentration occurred under hyper-osmotic conditions than under hypo-osmotic conditions. The concentrations of valine, isoleucine, lysine, glutamic acid, glycine, proline and taurine increased with rising salinity. The plasma levels of threonine, leucine, arginine, serine, and alanine showed a ‘U-shaped' relationship with salinity. The results of this study suggested that free amino acids might have important effects on osmotic acclimation in tongue sole.