Department of Biology, The August Krogh Centre, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark.
J Exp Biol. 2013 Apr 1;216(Pt 7):1235-43. doi: 10.1242/jeb.075531. Epub 2012 Dec 13.
Many species of tardigrades are known to tolerate extreme environmental stress, yet detailed knowledge of the mechanisms underlying the remarkable adaptations of tardigrades is still lacking, as are answers to many questions regarding their basic biology. Here, we present data on the inorganic ion composition and total osmotic concentration of five different species of tardigrades (Echiniscus testudo, Milnesium tardigradum, Richtersius coronifer, Macrobiotus cf. hufelandi and Halobiotus crispae) using high-performance liquid chromatography and nanoliter osmometry. Quantification of the ionic content indicates that Na(+) and Cl(-) are the principal inorganic ions in tardigrade fluids, albeit other ions, i.e. K(+), NH4(+), Ca(2+), Mg(2+), F(-), SO4(2-) and PO4(3-) were also detected. In limno-terrestrial tardigrades, the respective ions are concentrated by a large factor compared with that of the external medium (Na(+), ×70-800; K(+), ×20-90; Ca(2+) and Mg(2+), ×30-200; F(-), ×160-1040, Cl(-), ×20-50; PO4(3-), ×700-2800; SO4(2-), ×30-150). In contrast, in the marine species H. crispae, Na(+), Cl(-) and SO4(2-) are almost in ionic equilibrium with (brackish) salt water, while K(+), Ca(2+), Mg(2+) and F(-) are only slightly concentrated (×2-10). An anion deficit of ~120 mEq l(-1) in M. tardigradum and H. crispae indicates the presence of unidentified ionic components in these species. Body fluid osmolality ranges from 361±49 mOsm kg(-1) in R. coronifer to 961±43 mOsm kg(-1) in H. crispae. Concentrations of most inorganic ions are largely identical between active and dehydrated groups of R. coronifer, suggesting that this tardigrade does not lose large quantities of inorganic ions during dehydration. The large osmotic and ionic gradients maintained by both limno-terrestrial and marine species are indicative of a powerful ion-retentive mechanism in Tardigrada. Moreover, our data indicate that cryptobiotic tardigrades contain a large fraction of unidentified organic osmolytes, the identification of which is expected to provide increased insight into the phenomenon of cryptobiosis.
已知许多缓步动物物种能够耐受极端环境压力，但对于缓步动物惊人适应能力的潜在机制的详细了解仍然缺乏，并且它们的基础生物学的许多问题仍然没有答案。在这里，我们使用高效液相色谱法和纳米升渗透压计，提供了五种不同缓步动物（Echiniscus testudo、Milnesium tardigradum、Richtersius coronifer、Macrobiotus cf. hufelandi 和 Halobiotus crispae）的无机离子组成和总渗透压浓度的数据。离子含量的定量表明，Na(+)和 Cl(-)是缓步动物体液中的主要无机离子，但也检测到其他离子，如 K(+)、NH4(+)、Ca(2+)、Mg(2+)、F(-)、SO4(2-)和 PO4(3-)。在Limno-terrestrial 缓步动物中，与外部介质相比，各离子被高度浓缩（Na(+)，×70-800；K(+)，×20-90；Ca(2+)和 Mg(2+)，×30-200；F(-)，×160-1040；Cl(-)，×20-50；PO4(3-)，×700-2800；SO4(2-)，×30-150）。相比之下，在海洋物种 H. crispae 中，Na(+)、Cl(-)和 SO4(2-)几乎与（咸水）盐水处于离子平衡状态，而 K(+)、Ca(2+)、Mg(2+)和 F(-)的浓度则略有升高（×2-10）。在 M. tardigradum 和 H. crispae 中约 120 mEq l(-1)的阴离子缺乏表明这些物种中存在未识别的离子成分。体液渗透压范围从 R. coronifer 的 361±49 mOsm kg(-1)到 H. crispae 的 961±43 mOsm kg(-1)。R. coronifer 中活跃和脱水组之间的大多数无机离子浓度基本相同，这表明这种缓步动物在脱水过程中不会丢失大量无机离子。Limno-terrestrial 和海洋物种维持的大渗透压和离子梯度表明在缓步动物中存在强大的离子保留机制。此外，我们的数据表明，cryptobiotic 缓步动物含有大量未识别的有机渗透物，预计这些渗透物的鉴定将增加对cryptobiosis 现象的了解。
