Diatoms are microalgae that thrive in a range of habitats worldwide including polar areas. Remarkably, non-marine pennate diatoms do not create any morphologically distinct dormant stages that could help them to successfully face unfavourable conditions. Their survival is probably connected with the adaptation of vegetative cells to freezing and desiccation. Here we assessed the freezing tolerance of vegetative cells and vegetative-looking resting cells of 12 freshwater strains of benthic pennate diatoms isolated from polar habitats. To test the effect of various environmental factors, the strains were exposed to −20 °C freezing in four differently treated cultures: (1) vegetative cells growing in standard conditions in standard WC medium and (2) resting cells induced by cold and dark acclimation and resting cells, where (3) phosphorus or (4) nitrogen deficiency were used in addition to cold and dark acclimation. Tolerance was evaluated by measurement of basal cell fluorescence of chlorophyll and determination of physiological cell status using a multiparameter fluorescent staining. Four strains out of 12 were able to tolerate freezing in at least some of the treatments. The minority of cells appeared to be active immediately after thawing process, while most cells were inactive, injured or dead. Overall, the results showed a high sensitivity of vegetative and resting cells to freezing stress among strains originating from polar areas. However, the importance of resting cells for survival was emphasized by a slight but statistically significant increase of freezing tolerance of nutrient-depleted cells. Low numbers of surviving cells in our experimental setup could indicate their importance for the overwintering of diatom populations in harsh polar conditions.

硅藻是一种微藻，可以在包括极地地区在内的世界范围内的一系列栖息地中繁衍生息。值得注意的是，非海洋羽状硅藻不会产生任何形态上不同的休眠阶段，可以帮助它们成功面对不利条件。它们的存活可能与营养细胞对冷冻和干燥的适应有关。在这里，我们评估了从极地栖息地分离的 12 种底栖羽状硅藻淡水品系的营养细胞和看似营养的静息细胞的抗冻性。为了测试各种环境因素的影响，将菌株在四种不同处理的培养物中暴露于 -20°C 冷冻：（1）在标准 WC 培养基中在标准条件下生长的营养细胞和（2）冷和暗适应诱导的静息细胞和静息细胞，其中（3）磷或（4）缺氮除了寒冷和黑暗的驯化外。通过测量叶绿素的基底细胞荧光和使用多参数荧光染色确定生理细胞状态来评估耐受性。至少在一些治疗中，12 株中有 4 株能够耐受冷冻。少数细胞似乎在解冻过程后立即活跃，而大多数细胞不活跃、受伤或死亡。总体而言，结果表明，在来自极地地区的菌株中，营养细胞和静息细胞对冷冻应激具有很高的敏感性。然而，营养耗尽细胞的冷冻耐受性略有增加，但在统计学上显着增加了静息细胞对生存的重要性。