H2O2 and cytosolic Ca2+signals triggered by the PM H plus -coupled transport system mediate K+/Na+ homeostasis in NaCl-stressed Populus euphratica cells

Using confocal microscopy, X-ray microanalysis and the scanning ion-selective electrode technique, we investigated the signalling of H2O2, cytosolic Ca2+ ([Ca2+](cyt)) and the PM H+-coupled transport system in K+/Na+ homeostasis control in NaCl-stressed calluses of Populus euphratica. An obvious Na+/H+ antiport was seen in salinized cells; however, NaCl stress caused a net K+ efflux, because of the salt-induced membrane depolarization. H2O2 levels, regulated upwards by salinity, contributed to ionic homeostasis, because H2O2 restrictions by DPI or DMTU caused enhanced K+ efflux and decreased Na+/H+ antiport activity. NaCl induced a net Ca2+ influx and a subsequent rise of [Ca2+](cyt), which is involved in H2O2-mediated K+/Na+ homeostasis in salinized P. euphratica cells. When callus cells were pretreated with inhibitors of the Na+/H+ antiport system, the NaCl-induced elevation of H2O2 and [Ca2+](cyt) was correspondingly restricted, leading to a greater K+ efflux and a more pronounced reduction in Na+/H+ antiport activity. Results suggest that the PM H+-coupled transport system mediates H+ translocation and triggers the stress signalling of H2O2 and Ca2+, which results in a K+/Na+ homeostasis via mediations of K+ channels and the Na+/H+ antiport system in the PM of NaCl-stressed cells. Accordingly, a salt stress signalling pathway of P. euphratica cells is proposed.

利用共聚焦显微镜、X射线微量分析和扫描离子选择性电极技术，我们研究了胡杨在氯化钠胁迫的愈伤组织中，过氧化氢（H₂O₂）、胞质钙离子（[Ca²⁺]₍cyt₎）以及质膜氢离子耦合转运系统在钾离子/钠离子稳态控制中的信号传导。在盐渍化细胞中观察到明显的钠离子/氢离子逆向转运；然而，由于盐诱导的膜去极化，氯化钠胁迫导致了净钾离子外流。受盐度上调调节的H₂O₂水平有助于离子稳态，因为二苯碘翁（DPI）或二甲基硫脲（DMTU）对H₂O₂的限制导致钾离子外流增强以及钠离子/氢离子逆向转运活性降低。氯化钠诱导了净钙离子内流以及随后的[Ca²⁺]₍cyt₎升高，这参与了盐渍化胡杨细胞中H₂O₂介导的钾离子/钠离子稳态。当愈伤组织细胞用钠离子/氢离子逆向转运系统的抑制剂预处理时，氯化钠诱导的H₂O₂和[Ca²⁺]₍cyt₎升高相应地受到限制，导致更大的钾离子外流以及钠离子/氢离子逆向转运活性更显著的降低。结果表明，质膜氢离子耦合转运系统介导氢离子转运，并触发H₂O₂和Ca²⁺的胁迫信号传导，这通过介导氯化钠胁迫细胞的质膜中的钾离子通道和钠离子/氢离子逆向转运系统，导致钾离子/钠离子稳态。因此，提出了胡杨细胞的盐胁迫信号传导途径。