Effects of Salt Stress on the Activity and the Amount of Tonoplast H^+-ATPase from Pea Roots

To study the function and adaptive mechanism of tonoplast H + ATPase under salt stress, pea ( Pisum sativum L.) seedlings were treated with different concentrations of salt (100-250 mmol/L NaCl) and with 100 mmol/L NaCl for different days (1-3 d). The ATP hydrolytic activity and the proton transport activity and the changes of the amount of tonoplast H + ATPase (subunit A) were measured. ATP hydrolytic activity of H + ATPase prepared from plants treated with 250 mmol/L NaCl was reduced by about 25% compared to that of control plants, but that of stressed plants treated with 100 mmol/L and 200 mmol/L NaCl was unchanged. The activity from plants treated with 100 mmol/L NaCl for up to 3 d was lower than that of control plants by 20%. But the proton transport activity was increased under the same salt stresses as above. These results showed that the changes of the hydrolytic activity and the proton transport activity were not in proportion and salt stress may cause the change of the coupling ratio of H + transport activity to ATP hydrolysis. The protein amount kept unchanged and reduced a little only when pea was treated with 100 mmol/L NaCl for 3 d. These results indicated that salinity stimulated the increase of the pump efficiency of the V_ATPase from pea roots, which was due to the change of the coupling ratio, but not due to the increase of ATP hydrolysis and the amount of V_ATPase.

Changes of proton transportation across the inner mitochondrial membrane and H^+-ATPase in endotoxic shock rats

Objective: To investigate the changes of proton transportation across the inner mitochondrial membrane (IMM) and H + ATPase of hepatocytes in endotoxic shock rats. Methods: Endotoxin from E.Coil of 5.0 mg/kg or saline of 1 ml/kg was injected into the femoral vein. The rats were sacrificed pre injection and 1, 3, 5, 8 hours after injection, and plasma and liver tissue samples were collected respectively. The liver tissue samples were used for preparation of mitochondria and submitochondrial particles (SMPs). The proton translocation of SMPs and H + ATPase, phospholipase A 2 (PLA 2) activities and malondialdehyde (MDA) content, membrane fluidities of different level of mitochondria membrane and plasma MDA content were assayed. Results: (1) Five hours after E. Coli. O111B4 injection, the maximum fluorescence quenching ACMA after adding ATP, nicotinamide adenin dinucleoacid hydrogen (NADH), and the succinate were significantly decreased (P< 0.05 ). The time of maximum fluorescent quenching and the half time of fluorescent quenching were significantly prolonged (P< 0.01 ), especially when NADH was used as a substrate. (2) The mitochondrial H + ATPase activity was significantly increased at early stage of endotoxic shock (P< 0.05 ), and significantly decreased at late stage of endotoxic shock (P< 0.01 ). (3) The mitochondrial membrane bound PLA 2 activity, plasmal and mitochondrial MDA content were significantly increased and succinate dehydrogenase (SDH) activity of mitochondria decreased markedly in endotoxic shock rats (P< 0.05 ). (4) The mitochondrial membrane fluidity of different lipid regions was decreased, especially in the head of phospholipid. Conclusions: Proton transportation across IMM and mitochondrial H + ATPase activity are significantly decreased in endotoxic shock.