Effects Of NaCl Stress On The Activities Of Tonoplast H～+-ATPase And H～+-PPase In Roots, Stems And Leaves Of Suaeda Salsa

In a saline environment, salt-dilution halophytes alleviate salt toxicity through the capacity of sequestrating Na+ into the vacuole. The transportation of Na+ against the concentration gradient from the cytoplasm into the vacuole via the tonoplast Na+/H+ antiporter is dependent on the activities of tonoplast proton pumps (V-H+-ATPase and V-H+-PPase), which establish an electrochemical H+-gradient across the tonoplast that energizes the transporters. So vacuolar proton pumps possibly play a critical role in the compartmentalization of Na+ into the vacuole and salt tolerance in plants. In the present study, salt-dilution halophyte 5. salsa cultured under different salt concentrations was used to investigate the activities and subunits expression of V-H+-ATPase and V-H+-PPase in different organs of S. salsa by Western and Northern blot analysis in addition to the determination of some physiological parameters. The main results were shown as follows. 1. Effects of NaCl treatment on the growth of leaves, stems and roots of S. salsa.200 mmol/L NaCl markedly stimulated the growth of S. salsa seedlings, and the effects varied with different organs: the growth of leaves and stems was greatly stimulated by NaCl, while that of the roots was not affected under the same conditions. The results indicated the organ and tissue specificity in plant growth responses to NaCl stress.S. salsa plants have high capacity of accumulating Na+ in low Na+ concentration environment. The Na+ concentrations of cell sap from different organs were all greatly increased under 200 mmol/L NaCl treatment. And as a typical salt-accumulating halophyte, Na+ mainly accumulated in leaves and stems of 5". salsa under different salt treatment. About 93% of the total Na+ was stored in leaves and stems and only 7% in roots. The leaves and stems of 5. salsa are the main organs of Na+ accumulation so that the osmotic potential of the cell sap were much lower in leaves and stems than that in the roots under the same NaCl stress conditions. While K+ concentrations in the cell sap from different organs decreased significantly compared with the controls so that the Na+/K+ ratio markedly increased. Since the growth of S. salsa seedlings was promoted by salt stress, the decrease of K+ concentration in the cell sap to a certain extent won't inhibit the plants'growth. Roots, the role of which was not in ion accumulating, absorbed a large amount of Na+ and some K+ and then transported the majority of ions into leaves and stems of 5. salsa to modulate the osmolarity to maintain the normal growing state under salt stress.2. Effects of NaCl treatment on the activities and subunit expression of H+-ATPase in tonoplast vesicles prepared from different organs of S. salsa.V-H+-ATPase hydrolytic activity in different organs of both control and NaCl-treated S. salsa seedlings was: leaves > stems > roots. The V-H+-ATPase activities in leaves and stems were significantly increased, while it was only slightly enhanced in roots under NaCl treatment.Western blot analysis with the antibody against mung bean subunit A showed that in addition to the 70 kDa subunit, two additional polypeptides were also detected. It might be suspected that they were the hydrolyzed fragments of the 70 kDa subunit or the isoforms of subunit A. The subunit A was detected in all organs of S. salsa under NaCl treatments, but its protein amount was extremely low in roots.Western blot analysis of V-H+-ATPase in different organs of S. salsa with the antiserum ATP95 showed three polypeptides with apparent molecular masses of 70, 54 and 16 kDa. And the subunit pattern was not affected by NaCl stress though the protein amounts of subunit B and c were enhanced, and the expression of V-H+-ATPase subunit A in leaves and stems appeared no obvious difference under both conditions of control and 200 mmol/L NaCl treatment. The protein amounts of all the three subunjts are larger in leaves than that in stems, and it's the lowest in roots of 5. salsa.Northern blot analysis indicated that the transcription...