Mechanism of the effect of polyamines on the activity of tonoplasts of barley roots under salt stress

The seeds of barley (Hordeum vulgare L. cv. Jian 4) were soaked with 0.1 mmol/L putrescine (Put) and 0.5 mmol/L spermidine (Spd), and then the seedlings were treated with 200 mmol/L NaCl. The growth rate (GR), dry matter accumulation, distribution of ions, the amount of polyamines (PAs) bound to. tonoplast proteins as well as lipid composition and the activity of tonoplast vesicles isolated from roots were investigated. The results showed that soaking with Put or Spd could retard salt injury, promote GR and dry matter accumulation, and increase K+/Na+ in the roots. Compared with NaCl-treated plants, phospholipid content in root tonoplast rose by soaking with Put and Spd, while the level of galactose in lipids was decreased. Moreover, the ratio in noncovalently conjugated PA contents of (Spd + PAx (an unknown PA)) to (Put + Dap (diaminopropane)), and the total contents of covalently and noncovalently conjugated PAs were all increased. Statistical analysis indicated that the ratio of ( Spd + PAx) to (Put + Dap) was significantly and positively correlated with the activities of membrane associated enzymes H+-ATPase and H+-PPase.