Sciandra Théo, Forget Marie-Hélène, Bruyant Flavienne, Béguin Marine, Lacour Thomas, Bowler Chris, Babin Marcel
Takuvik International Research Laboratory, Université Laval (Canada) & CNRS (France), Département de Biologie and Québec-Océan, Université Laval, Québec, Canada.
Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Ecole Normale Supérieure, CNRS, INSERM, Université PSL, Paris, 75005, France.
J Phycol. 2022 Apr;58(2):281-296. doi: 10.1111/jpy.13232. Epub 2022 Feb 3.
At high latitudes, the polar night poses a great challenge to photosynthetic organisms that must survive up to six months without light. Numerous studies have already shed light on the physiological changes involved in the acclimation of microalgae to prolonged darkness and subsequent re-illumination. However, these studies have never considered inter-individual variability because they have mainly been conducted with bulk measurements. On the other hand, such long periods are likely to impact within-population selection processes. In this study, we hypothesized that distinct subpopulations with specific traits may emerge during acclimation of a population of diatoms to darkness. We addressed this hypothesis using flow cytometry (FCM), which allow to individually characterize large numbers of cells. The ecologically dominant polar pennate diatom Fragilariopsis cylindrus was subjected to three dark acclimation (DA) experiments of one, three, and five months duration, during which all cultures showed signs of recovery once light became available again. Our results suggest that darkness survival of F. cylindrus relies on reduction of metabolic activity and consumption of carbon reserves. In addition, FCM allowed us to record three different causes of death, each shared by significant numbers of individuals. The first rendered cells were unable to survive the stress caused by the return to light, probably due to a lack of sufficient photoprotective defenses. The other two were observed in two subpopulations of cells whose physiological state deviated from the original population. The data suggest that starvation and failure to maintain dormancy were the cause of cell mortality in these two subpopulations.
在高纬度地区，极夜对光合生物构成了巨大挑战，这些生物必须在无光条件下存活长达六个月。众多研究已经揭示了微藻适应长期黑暗及随后重新光照过程中所涉及的生理变化。然而，这些研究从未考虑个体间的变异性，因为它们主要是通过批量测量进行的。另一方面，如此长的时期可能会影响种群内部的选择过程。在本研究中，我们假设在硅藻种群适应黑暗的过程中可能会出现具有特定特征的不同亚种群。我们使用流式细胞术（FCM）来验证这一假设，流式细胞术能够对大量细胞进行个体特征分析。生态上占主导地位的极地舟形硅藻纤细角毛藻进行了为期1个月、3个月和5个月的三次黑暗适应（DA）实验，在此期间，一旦再次有光照，所有培养物都显示出恢复的迹象。我们的结果表明，纤细角毛藻在黑暗中的存活依赖于代谢活动的降低和碳储备的消耗。此外，流式细胞术使我们能够记录三种不同的死亡原因，每种原因都有大量个体出现。第一种情况是细胞无法在恢复光照所造成的压力下存活，这可能是由于缺乏足够的光保护防御机制。另外两种情况在两个生理状态偏离原始种群的细胞亚群中观察到。数据表明，饥饿和无法维持休眠是这两个亚群中细胞死亡的原因。
