真菌在生长过程中通常要维持500kPa的内部膨压，然而，真菌在生长期间不可避免地遭受渗透刺激，生物体通过调节膨压维持一个跨膜的渗透梯度来驱动细胞伸长。丝裂原活化蛋白激酶 (MAPK)是生物体内重要的信号转导系统之一，能够调节细胞的渗透压。

真菌对高渗的应激中电信号发生了快速反应，膨压恢复前(10-60min)出现短暂的去极化(1-2min)，紧接着出现持续的超极化(5-10min)。澳大利亚著名微生物学家Lew建立了一种基于非损伤微测技术的研究方法，发现短暂的去极化是由Ca²⁺内流引起，持续的超极化是由于H⁺外流引起。渗透突变体os-1的膨压比野生型低，高渗处理后没有持续的超极化，两者的离子流有显著差异，os-1的Cl^-吸收增加，K⁺流几乎不变，H⁺外流下降。

通过离子流研究，结合分子生物学实验说明MAPK能够调节离子转运，活化H⁺-ATPase以及调节K⁺和Cl^-的吸收。这项研究为人们认识细胞如何通过蛋白的作用控制离子流，最终调节细胞的膨压来适应环境中的渗透胁迫提供了证据，Ca²⁺在其中的调控作用将会得到进一步研究。

关键词：丝裂原活化蛋白激酶(mitogen-activated protein kinases,MAPK);膨压(Turgor);离子流(Ion flux);真菌(Fungi)

参考文献：Lew RR, et al. Eukaryotic cell, 2006,5,480-487

Role of a Mitogen-Activated Protein Kinase Cascade in Ion Flux-Mediated Turgor Regulation in Fungi

Roger R. Lew,^1,* Natalia N. Levina,¹ Lana Shabala,² Marinela I. Anderca,¹ and Sergey N. Shabala^2,

Department of Biology, York University, Toronto, Ontario, Canada,¹ School of Agricultural Science, University of Tasmania, Hobart, Australia²

Received 1 October 2005/ Accepted 20 December 2005

ABSTRACT:

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 Ca²⁺ 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.