杜氏盐藻质膜ATPase在渗透调节中的可能作用

Role of the Plasma Membrane H^+-ATPase During the Osmoregulation of the Alga Dunaliella salina Under Hypertonic Stress

杜氏盐藻是一种以甘油为渗透调节物质的单细胞海藻,能够在0.08～5.0mol/L NaGl的培养液中生长。当外界NaGl浓度从0.5mol/L上升到4.0mol/L时,藻细胞内的Na^+和K^+含量变化不大,甘油含量则从6.20Pg/cell上升到51.50pg/cell。当藻细胞承受2.0mol/L到3.0mol/L NaCl的高渗胁迫时,能通过增加细胞内甘油含量来恢复原有形态;同时,藻细胞的H^+分泌增加,ATP含量下降;20μmol/L Na_3VO_4抑制了这些变化。KGN处理虽降低藻细胞内的ATP含量,却增加K^+外流和Na^+内渗。

The motile unicellular halotolerant alga Dunaliella salina, which can grow in media containing 0.08～~5.0 mol/L NaCl (Fig. 1), osmoregulated mostly by accumulating intracellularly a single compatible solute, glycerol (Fig. 3). With the increase of the extracellular NaCl concentrations from 0.50～4.0 mol/L, the amount of the intracellular glycerol rose markedly from 6.20～51.5 pg/cell (Fig. 3) and the intracellular Na^+ and K^+ contents had a small range of variation, around 30 and 35 mmol/L (Fig. 2) respectively. During a hypertonic treatment from 2.0 mol/L to 3.0 mol/L NaCl solution, the alga could recover their original volumes by raising their intracellular glycerol content in about 1h (Figs. 5,6). At the same time, the intracellular ATP content decreased (Fig. 8) and the H^+ secretion from the alga cells increased (Fig. 7). All of these changes could be fully inhi bited by 20 μmol / L Na_3VO_4, a specific inhibitor of the DM H^+-ATPase (Figs. 7,8).Thus it is suggested that the activity of the PM H^+-ATPase is stimulated by hypertonic stress and plays a central role in the ajustment of the alga against the stress. In a 2.0 mol/L NaCl medium, the increase of the intracellular Na^+ content and the decreases of the intracellular K^+ and ATP contents resulting from the treatment with 3.0 mmol/L KCN also show the important role played by the Phi H^+-ATPase of the alga against extracellular osmotic pressure (Fig. 9). The mechanism by which the PM H^+-APTase participates in the activition of glycerol synthesis in the alga is discussed.