Lew Roger R, Levina Natalia N, Shabala Lana, Anderca Marinela I, Shabala Sergey N
Department of Biology, York University, 4700 Keele Street, Toronto, Ontario M3J 1P3, Canada.
Eukaryot Cell. 2006 Mar;5(3):480-7. doi: 10.1128/EC.5.3.480-487.2006.
Fungi normally maintain a high internal hydrostatic pressure (turgor) of about 500 kPa. In response to hyperosmotic shock, there are immediate electrical changes: a transient depolarization (1 to 2 min) followed by a sustained hyperpolarization (5 to 10 min) prior to turgor recovery (10 to 60 min). Using ion-selective vibrating probes, we established that the transient depolarization is due to Ca(2+) influx and the sustained hyperpolarization is due to H(+) efflux by activation of the plasma membrane H(+)-ATPase. Protein synthesis is not required for H(+)-ATPase activation. Net K(+) and Cl(-) uptake occurs at the same time as turgor recovery. The magnitude of the ion uptake is more than sufficient to account for the osmotic gradients required for turgor to return to its original level. Two osmotic mutants, os-1 and os-2, homologs of a two-component histidine kinase sensor and the yeast high osmotic glycerol mitogen-activated protein (MAP) kinase, respectively, have lower turgor than the wild type and do not exhibit the sustained hyperpolarization after hyperosmotic treatment. The os-1 mutant does not exhibit all of the wild-type turgor-adaptive ion fluxes (Cl(-) uptake increases, but net K(+) flux barely changes and net H(+) efflux declines) (os-2 was not examined). Both os mutants are able to regulate turgor but at a lower level than the wild type. Our results demonstrate that a MAP kinase cascade regulates ion transport, activation of the H(+)-ATPase, and net K(+) and Cl(-) uptake during turgor regulation. Other pathways regulating turgor must also exist.
真菌通常维持约500 kPa的高内部静水压力（膨压）。响应高渗休克时，会立即发生电变化：短暂去极化（1至2分钟），随后在膨压恢复（10至60分钟）之前出现持续的超极化（5至10分钟）。使用离子选择性振动探针，我们确定短暂去极化是由于Ca(2+)内流，而持续超极化是由于质膜H(+)-ATP酶激活导致H(+)外流。H(+)-ATP酶激活不需要蛋白质合成。净K(+)和Cl(-)摄取与膨压恢复同时发生。离子摄取的幅度足以解释膨压恢复到其原始水平所需的渗透梯度。两个渗透突变体os-1和os-2，分别是双组分组氨酸激酶传感器和酵母高渗甘油丝裂原活化蛋白（MAP）激酶的同源物，其膨压低于野生型，并且在高渗处理后不表现出持续的超极化。os-1突变体没有表现出所有野生型的膨压适应性离子通量（Cl(-)摄取增加，但净K(+)通量几乎不变，净H(+)外流下降）（未检测os-2）。两个os突变体都能够调节膨压，但水平低于野生型。我们的结果表明，MAP激酶级联在膨压调节过程中调节离子转运、H(+)-ATP酶的激活以及净K(+)和Cl(-)摄取。必然还存在其他调节膨压的途径。
