Frieder Christina A, Applebaum Scott L, Pan T-C Francis, Manahan Donal T
Biol Bull. 2018 Feb;234(1):45-57. doi: 10.1086/696830. Epub 2018 Mar 2.
Exogenous environmental factors alter growth rates, yet information remains scant on the biochemical mechanisms and energy trade-offs that underlie variability in the growth of marine invertebrates. Here we study the biochemical bases for differential growth and energy utilization (as adenosine triphosphate [ATP] equivalents) during larval growth of the bivalve Crassostrea gigas exposed to increasing levels of experimental ocean acidification (control, middle, and high pCO, corresponding to ∼400, ∼800, and ∼1100 µatm, respectively). Elevated pCO hindered larval ability to accrete both shell and whole-body protein content. This negative impact was not due to an inability to synthesize protein per se, because size-specific rates of protein synthesis were upregulated at both middle and high pCO treatments by as much as 45% relative to control pCO. Rather, protein degradation rates increased with increasing pCO. At control pCO, 89% of cellular energy (ATP equivalents) utilization was accounted for by just 2 processes in larvae, with protein synthesis accounting for 66% and sodium-potassium transport accounting for 23%. The energetic demand necessitated by elevated protein synthesis rates could be accommodated either by reallocating available energy from within the existing ATP pool or by increasing the production of total ATP. The former strategy was observed at middle pCO, while the latter strategy was observed at high pCO. Increased pCO also altered sodium-potassium transport, but with minimal impact on rates of ATP utilization relative to the impact observed for protein synthesis. Quantifying the actual energy costs and trade-offs for maintaining physiological homeostasis in response to stress will help to reveal the mechanisms of resilience thresholds to environmental change.
外源环境因素会改变生长速率，然而，关于海洋无脊椎动物生长变异性背后的生化机制和能量权衡的信息仍然很少。在这里，我们研究了双壳贝类太平洋牡蛎幼虫在实验性海洋酸化水平不断升高（对照、中度和高度pCO₂，分别对应约400、约800和约1100 μatm）的情况下，差异生长和能量利用（以三磷酸腺苷[ATP]当量计）的生化基础。升高的pCO₂阻碍了幼虫积累贝壳和全身蛋白质含量的能力。这种负面影响并非由于本身无法合成蛋白质，因为在中度和高度pCO₂处理下，相对于对照pCO₂，特定大小的蛋白质合成速率上调了多达45%。相反，蛋白质降解速率随着pCO₂的升高而增加。在对照pCO₂条件下，幼虫细胞能量（ATP当量）利用的89%仅由两个过程构成，其中蛋白质合成占66%，钠钾转运占23%。蛋白质合成速率升高所必需的能量需求可以通过从现有ATP库中重新分配可用能量或通过增加总ATP的产生来满足。前一种策略在中度pCO₂条件下观察到，而后一种策略在高度pCO₂条件下观察到。升高的pCO₂也改变了钠钾转运，但相对于蛋白质合成所观察到的影响，对ATP利用速率的影响最小。量化应对压力时维持生理稳态的实际能量成本和权衡将有助于揭示对环境变化的恢复力阈值机制。
