Kisnieriene Vilma, Lapeikaite Indre, Pupkis Vilmantas, Beilby Mary Jane
Department of Neurobiology and Biophysics, Life Sciences Center, Institute of Biosciences, Vilnius University, Vilnius, Lithuania.
School of Physics, The University of NSW, Sydney, NSW, Australia.
Front Plant Sci. 2019 Feb 18;10:82. doi: 10.3389/fpls.2019.00082. eCollection 2019.
Action potentials (AP) of characean cells were the first electrical transients identified in plants. APs provide information about plethora of environmental cues. Salinity stress is critical for plants and impacts on excitability. The AP of brackish Characeae , obtained in artificial pond water (APW) and under osmotic stress of 90 or 180 mM sorbitol APW or saline stress of 50 or 100 mM NaCl APW, were simulated by the Thiel-Beilby model (Beilby and Al Khazaaly, 2016). The model is based on a paradigm from animal systems, featuring the second messenger inositol 1,4,5-triphosphate (IP) mediating the opening of Ca channels on internal stores. In plants the IP receptors have not been identified, so other second messengers might translate the threshold plasma membrane depolarization to Ca release. The increased Ca concentration in the cytoplasm activates Cl channels, which lead to the depolarizing phase of the AP. The repolarization to normal resting potential difference (PD) results from the Ca being re-sequestered by the Ca pumps, the closure of the Cl channels, efflux of K through the depolarization-activated outward rectifier channels and the continuing activity of the proton pump. The AP form is longer in APW compared to that of , with more gradual repolarization. The tonoplast component of the AP is larger than that in . The plasma membrane AP is prolonged by the exposure to saline to a "rectangular" shape, similar to that in . However, the changes are more gradual, allowing more insight into the mechanism of the process. It is possible that the cells recover the original AP form after prolonged exposure to brackish conditions. Some cells experience tonoplast APs only. As in , the proton pump is transiently inhibited by the high cytoplasmic Ca and gradually declines in saline media. However, if the cells are very hyperpolarized at the start of the experiment, the pump inhibition both by the AP and by the saline medium is mitigated. The model parameters and their changes with salinity are comparable to those in .
轮藻细胞的动作电位（AP）是植物中最早被识别的电瞬变现象。动作电位提供了大量有关环境线索的信息。盐度胁迫对植物至关重要，并影响其兴奋性。在人工池塘水（APW）中以及在90或180 mM山梨醇APW的渗透胁迫或50或100 mM NaCl APW的盐胁迫下获得的微咸轮藻科植物的动作电位，由蒂尔-比尔比模型（Beilby和Al Khazaaly，2016）进行模拟。该模型基于动物系统的一个范式，其特征是第二信使肌醇1,4,5-三磷酸（IP）介导内部储存库上钙通道的开放。在植物中尚未鉴定出IP受体，因此其他第二信使可能会将阈值质膜去极化转化为钙释放。细胞质中钙浓度的增加会激活氯通道，从而导致动作电位的去极化阶段。恢复到正常静息电位差（PD）是由于钙被钙泵重新隔离、氯通道关闭、钾通过去极化激活的外向整流通道外流以及质子泵的持续活动。与[未提及的对照情况]相比，在APW中的动作电位形式更长，复极化更平缓。动作电位的液泡膜成分比[未提及的对照情况]中的更大。质膜动作电位通过暴露于盐中而延长为“矩形”形状，类似于[未提及的对照情况]中的。然而，变化更为平缓，这使得对该过程的机制有了更多了解。长时间暴露于微咸条件后，细胞有可能恢复原来的动作电位形式。一些细胞仅经历液泡膜动作电位。与[未提及的对照情况]一样，质子泵会被高细胞质钙短暂抑制，并在盐培养基中逐渐下降。然而，如果细胞在实验开始时非常超极化，动作电位和盐培养基对泵的抑制作用都会减轻。模型参数及其随盐度的变化与[未提及的对照情况]中的相当。
