Generation And Interaction Of Endogenous Reactive Oxygen Species On Physiological And Biochemical Characters In Wheat Seedlings Exposed To Salt Stress

Ion toxicity and oxidative damage caused by high salinity have an adverse effects on plant growth and development as well as crop yield, which resulted in the inhibition of agricultural production and restriction of farmers? living standard. Nitric oxide?NO? and reactive oxygen species?ROS? are critical signaling molecules located in the central part of stresses signal transduction and involved in regulating a variety of physiological and biochemical processes during plant responses to abiotic stresses. The present work used wheat?Triticum aestivum L., cv Xihan3? seedlings to investigate the reciprocal effect between endogenous NO and ROS generation and to explore the regulative effects of them on seedling growth and changes of Na, K, Ca contents as well as antioxidative responses in wheat seedlings under Na Cl treatment with or without2-phenyl-4,4,5,5,-tetramethylimidazoline-3-oxide-1-oxyl?PTIO?, catalase?CAT? or diphenylene iodonium?DPI?, trying to explore the roles and mechanisms of interaction between NO and ROS signaling in adaptive responses to salt stress in wheat seedlings. The main results were presented as follows:1. Low salinity stimulated seedling growth, whereas high salinity reduced the lengths of roots and shoots in wheat seedlings. Endogenous NO scavenging by PTIO and apoplastic H₂O₂ eliminating by exogenous CAT partly alleviated Na Cl-inhibitory effects on seedling growth, while Na Cl+DPI?a widely used NADPH oxidase inhibitor? treatment led to the most prominent inhibition in seedling growth.2. All salinity concentrations resulted in the increase of Na content and the decreases of Ca level and K/Na value in wheat seedlings; differently, the amount of K reduced in roots but elevated in leaves only in 50 mmol·L-1 Na Cl-stressed seedlings. In comparison with150 mmol·L-1 Na Cl treatment alone, the presence of PTIO, CAT or DPI decreased root Na and Ca contents but increased these two parameters in leaves in salinity-treated seedlings. In contrast, K content rose in response to Na Cl treatment together with PTIO or CAT but lowered to Na Cl+DPI in roots, and K level increased in leaves in the presence of these three reagents.3. Salinity induced significant elevation of NO in wheat roots, which could be reversed by PTIO or CAT. The activity of nitric oxide synthase?NOS?-like proteins decreased in 50mmol·L-1 Na Cl-treated roots but increased due to 150 mmol·L-1 Na Cl, which could be further stimulated by PTIO or CAT. However, the maximum increases of NO content and fluorescence together with the highest activity of NOS-like proteins were found in Na Cl+DPI-treated roots.4. Malondialdehyde?MDA?, total and apoplastic ROS contents significantly rose in salt-treated wheat roots. Compared with 150 mmol·L-1 Na Cl treatment alone, the application of PTIO led to the decreases of MDA, total ROS and apoplastic hydrogen peroxide?H₂O₂?, superoxide anion(O₂^??) contents along with the increase of hydroxyl radical?·OH? level in the apoplast of wheat roots. Na Cl stress in combination with CAT significantly decreased MDA and total ROS contents but further increased apoplastic O₂^??content in wheat roots. In addition, the decreases of total H₂O₂ and ·OH contents as well as apoplastic O₂^?? level along with the increases of MDA, total O₂^??, apoplastic H₂O₂ and ·OH contents were observed in Na Cl+DPI-treated wheat roots.5. The increases of total and apoplastic superoxide dismutase?SOD?, CAT activities and the decreases of total peroxidase?POD?, ascorbate peroxidase?APX?, glutathione reductase?GR? activities together with the inhibition of apoplastic POD and APX were observed in salt-treated wheat roots. Compared with 150 mmol·L-1 Na Cl stress alone, salinity stress together with PTIO resulted in significant decreases of total SOD, POD, CAT and APX activities as well as apoplastic SOD, POD and GR activities but further increased total GR and apoplastic CAT activities in wheat roots, the use of exogenous CAT decreased total SOD, POD activities as well as apoplastic POD, GR activities but enhanced total APX and apoplastic SOD, APX activities, DPI addition stimulated total SOD, APX and GR activities but obviously inhibited apoplastic SOD, POD, CAT and GR activities in salinity-stressed roots.6. Salinity stress had an inhibition of cell wall-bound POD?cw-POD?, diamine oxidase?DAO? and polyamine oxidase?PAO? activities in wheat roots. The application of PTIO or CAT led to the decrease of cw-POD activity but obviously stimulated DAO and PAO activities in 150 mmol·L-1 Na Cl-treated wheat roots. In addition, Na Cl+DPI treatment significantly enhanced cw-POD, DAO and PAO activities in wheat roots.Taken together, low salinity stimulated seedling growth while higher salinity reduced the lengths of roots and shoots in wheat seedlings. Different Na Cl concentrations caused the increase of Na content and the decreases of Ca level and K/Na value in wheat seedlings.Salinity-induced NO accumulation and ROS generation influenced each other and both of them might be played interactive roles in the regulation of Na, K, Ca absorption and translocation of these elements to aboveground plant parts as well as antioxidant enzyme activities in wheat roots under Na Cl treatment, in order to maintain the balance of ion contents and redox in plants, then alleviated the damage caused by salinity of wheat seedlings.