School of Agricultural Science, University of Tasmania, Private Bag 54, Hobart, Tas. 7001, Australia.
Environ Microbiol. 2009 Jul;11(7):1835-43. doi: 10.1111/j.1462-2920.2009.01908.x.
A non-invasive ion-selective microelectrode technique was used to elucidate the ionic mechanisms of osmotic adjustment in a marine protist thraustochytrid. Hypoosmotic stress caused significant efflux of Na(+), Cl(-) and K(+) from thraustochytrid cells. Model calculations showed that almost complete osmotic adjustment was achieved within the first 30 min after stress onset. Of these, sodium was the major contributor (more than half of the total osmotic adjustment), with chloride being the second major contributor. The role of K(+) in the process of osmotic adjustment was relatively small. Changes in Ca(2+) and H(+) flux were attributed to intracellular signalling. Ion flux data were confirmed by growth experiments. Thraustochytrium cells showed normal growth patterns even when grown in a sodium-free solution provided the medium osmolality was adjusted by mannitol to one of the seawater. That suggests that the requirement of sodium for thraustochytrid growth cycle is due to its role in cell osmotic adjustment rather than because of the direct Na(+) involvement in cell metabolism. Altogether, these data demonstrate the evidence for turgor regulation in thraustochytrids and suggest that these cells may be grown in the absence of sodium providing that cell turgor is adjusted by some other means.
采用非侵入性离子选择性微电极技术阐明了海洋原生动物甲藻渗透调节的离子机制。低盐胁迫导致甲藻细胞中 Na(+)、Cl(-)和 K(+)大量外流。模型计算表明，在胁迫开始后的头 30 分钟内几乎完成了完全的渗透调节。其中，钠是主要贡献者（超过总渗透调节的一半），氯是第二大贡献者。K(+)在渗透调节过程中的作用相对较小。Ca(2+)和 H(+)通量的变化归因于细胞内信号转导。离子通量数据通过生长实验得到了证实。即使在没有钠离子的溶液中培养，只要培养基渗透压通过甘露醇调节至与海水相同的渗透压，甲藻细胞仍能正常生长。这表明，钠对于甲藻生长周期的需求是由于其在细胞渗透调节中的作用，而不是因为 Na(+)直接参与细胞代谢。总之，这些数据证明了甲藻中膨压调节的存在，并表明这些细胞可以在没有钠的情况下生长，只要通过其他方式调节细胞膨压。
