Physiological And Biochemical Response Of Spring Wheat Varieties Longchun 30 And Longchun 27 Under Salt Stress

Soil salinization seriously affects the development of agricultural production and ecological environment, which limits different physiological and biochemical processes in plants including seed germination and seedling growth and development. Studying salt tolerance mechanisms of plant and finding suitable varieties are of great significance to utilize saline land and improve ecological environment. In the present study, new spring wheat(cv Longchun 30 and Longchun 27) seedlings are used to investigate changes of reactive oxygen species(ROS) level, antioxidate enzyme activities, ascorbate-glutathione cycle and proline metabolism in response to Na Cl stress, trying to investigate response mechanisms of plant under salt stress. The main results are as follows:1. The inhibition of germination was observed only in 200 mmol · L-1 Na Cl-stressed Longchun 30 seeds; 25 mmol · L-1 salt treatment induced an increase of root and stem growth only in Longchun 30 seedlings but no significant change of these parameters in Longchun 27 ones, while 100 and 200 mmol · L-1 Na Cl stress resulted in decreased root and stem growth in two wheat seedlings. Additionally, there were no changes of chlorophyll a, chlorophyll b and total chlorophyll contents in two wheat seedlings exposed to Na Cl stress.2. Increased hydrogen peroxide(H2O2) and superoxide anion(O2?) due to all Na Cl concentrations in Longchun 30 roots but due to 100 and 200 mmol · L-1 Na Cl treatment in Longchun 27 ones as well as elevated hydroxyl radical(·OH) caused by 200 mmol · L-1Na Cl in two wheat roots were observed. Moreover, salt stress induced different degree changes of apoplastic ROS contents in two wheat roots. Compared with the control,molondialdehyde(MDA) content in Longchun 30 roots exposed to Na Cl stress were lower, while an increase of MDA level was found in 200 mmol · L-1 Na Cl-stressed Longchun 27 ones. Salinity stress inhibited activities of cell wall-bound peroxidase,diamine oxidase(DAO) and polyamine oxidase(PAO) in two wheat roots.3. Activities of superoxide dismutase(SOD) and peroxidase(POD) elevated in 100 and 200 mmol · L-1 Na Cl treated-roots of Longchun 30 seedlings, whereas only root POD activity increased in Longchun 27 seedlings exposed to 25 mmol · L-1 Na Cl. Moreover, induced catalase(CAT) activity and inhibited apoplastic SOD, POD and CAT were detected in two wheat roots after salinity treatment.4. Increased ascorbate(As A) content and glutathione reducase(GR) activity as well as decreased and then increased glutathione(GSH) levels and ascorbate peroxidate(APX)activity were observed in two wheat roots under Na Cl stress. Moreover,monodehydroascortate reduetase(MDHAR) activity rose only in 25 and 100 mmol · L-1Na Cl-treated Longchun 30 roots, and increased dehydrooascorbate reductase(DHAR)activity due to all Na Cl concentrations in Longchun 30 roots but to 100 and 200 mmol · L-1 Na Cl in Longchun 27 ones were observed. Additionally, ascorbate oxidase(AAO) activity inhibited in Longchun 30 roots but induced in Longchun 27 ones.5. Salt stress induced the accumulation of proline content and a decrease of glutamate kinase(GK) activity in two wheat roots. And ornithine ?-aminotransferase(OAT) activity increased in Longchun 30 roots exposed to 200 mmol · L-1 Na Cl and in Longchun 27 ones treated with 25 and 200 mmol · L-1 Na Cl. In addition, decreased proline dehydrogenase(PDH) activity due to 100 and 200 mmol · L-1 Na Cl in Longchun 30 roots but to all Na Cl concentrations in Longchun 27 ones were observed.In conclusion, our results suggested that changes of seed germination and seedling growth in response to salt stress were different in two wheats, and the growth inhibition of two wheat seedlings might be associated with the excessive generation of ROS; the accumulation of ROS in Logchun 30 were more sensitive to lower salinity stress in comparison with Longchun27 ones. Decreased cell wall bound-POD, DAO and PAO activities as well as increased antioxidate enzyme activities(SOD, POD, CAT, APX and GR in Longchun 30 roots; CAT,APX and GR in Longchun 27 roots) and the non enzymatic antioxidant contents(As A, GSH and proline) could alleviated the damage induced by ROS in two wheat roots under Na Cl stress. Moreover, accumulation of As A in Longchun 30 roots were associated with inhibited AAO activity and increased MDHAR and DHAR activities, while only enhanced DHAR activity might result in an increase of As A level in Longchun 27 ones. In addition, proline accumulation in Longchun 27 roots may be associated with increased OAT activity and decreased PDH activity but associated with reduced PDH activity in Longchun 30 ones, while glutamic synthesis pathway is not responsible for the increase of proline content in two wheat roots under salinity stress.