Physiological response of ryegrass seedlings to NaHCO_3 stress

Ryegrass seedlings were exposed to Hoagland′s nutrient solution with NaHCO3 added(0,50,100,150,200 mmol/L),and the effects of NaHCO3 stress on the plant growth,metabolism of reactive oxygen species(ROS) and osmotica accumulation in leaves were studied by a sandy culture.The results showed(1) With the increasing of NaHCO3 concentration,the fresh and dry weights of the seedlings decreased,the contents of O2 ·,H2O2,MDA and Na+ in leaves increased gradually,and the activities of CAT and POD,the contents of AsA,GSH and K+ as well as K+/Na+ decreased continually,and the activities of SOD and APX exhibited a humped-curve,while the activities of V-H+-ATPase and V-H+-PPase were higher than the control at 50~150 mmol/L NaHCO3 but lower than the control at 200 mmol/L NaHCO3.(2) Alkali-stress decreased the contents of soluble protein and free amino acid while increased the contents of soluble sugar and proline in the seedling leaves.It was concluded that the imbalances of ROS metabolism and Na+ to K+ in the seedling leaves were possibly caused by alkaline stress,and consumed more energy for osmotic adjustment by accumulating organic solutes,which might be an important reason that the growth of ryegrass seedlings under alkaline stress was inhibited.