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Eukaryotic Cell MAPK通過調(diào)節(jié)離子流來改變細(xì)胞的膨壓 | |
| MAPK在離子流調(diào)節(jié)真菌膨壓中的作用
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 上圖： 野生型和os-1突變體真菌菌絲在高滲處理下的H+、K+、Cl-、Ca2+離子流。負(fù)值表示離子外流，正值表示離子內(nèi)流，圓形的是野生型，三角形的是os-1突變體。 真菌在生長過程中通常要維持500kPa的內(nèi)部膨壓，然而，真菌在生長期間不可避免地遭受滲透刺激，生物體通過調(diào)節(jié)膨壓維持一個跨膜的滲透梯度來驅(qū)動細(xì)胞伸長。絲裂原活化蛋白激酶 (MAPK)是生物體內(nèi)重要的信號轉(zhuǎn)導(dǎo)系統(tǒng)之一，能夠調(diào)節(jié)細(xì)胞的滲透壓。 真菌對高滲的應(yīng)激中電信號發(fā)生了快速反應(yīng)，膨壓恢復(fù)前(10-60min)出現(xiàn)短暫的去極化(1-2min)，緊接著出現(xiàn)持續(xù)的超極化(5-10min)。澳大利亞著名微生物學(xué)家Lew建立了一種基于非損傷微測技術(shù)的研究方法，發(fā)現(xiàn)短暫的去極化是由Ca2+內(nèi)流引起，持續(xù)的超極化是由于H+外流引起。滲透突變體os-1的膨壓比野生型低，高滲處理后沒有持續(xù)的超極化，兩者的離子流有顯著差異，os-1的Cl-吸收增加，K+流幾乎不變，H+外流下降。 通過離子流研究，結(jié)合分子生物學(xué)實驗說明MAPK能夠調(diào)節(jié)離子轉(zhuǎn)運(yùn)，活化H+-ATPase以及調(diào)節(jié)K+和Cl-的吸收。這項研究為人們認(rèn)識細(xì)胞如何通過蛋白的作用控制離子流，最終調(diào)節(jié)細(xì)胞的膨壓來適應(yīng)環(huán)境中的滲透脅迫提供了證據(jù)，Ca2+在其中的調(diào)控作用將會得到進(jìn)一步研究。 | |
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. Shabala2,
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.