Chen Bokun, Liu Jihua, Xu Ge, Li Gang
Institute of Marine Science and Technology, Shandong University, Qingdao 266237, China.
Joint Laboratory for Ocean Research and Education of Dalhousie University, Shandong University and Xiamen University, Qingdao 266237, China.
Microorganisms. 2021 Dec 9;9(12):2541. doi: 10.3390/microorganisms9122541.
Exacerbating deoxygenation is extensively affecting marine organisms, with no exception for phytoplankton. To probe these effects, we comparably explored the growth, cell compositions, photosynthesis, and transcriptome of a diatom under a matrix of O levels and Light:Dark cycles at an optimal growth light. The growth rate (μ) of under a 8:16 L:D cycle was enhanced by 34% by low O but reduced by 22% by hypoxia. Under a 16:8 L:D cycle, however, the μ decreased with decreasing O level. The cellular Chl content decreased with decreasing O under a 8:16 L:D cycle, whereas the protein content decreased under a 16:8 L:D cycle. The prolonged photoperiod reduced the Chl but enhanced the protein contents. The lowered O reduced the maximal PSII photochemical quantum yield (F/F), photosynthetic oxygen evolution rate (Pn), and respiration rate (Rd) under the 8:16 or 16:8 L:D cycles. Cellular malondialdehyde (MDA) content and superoxide dismutase (SOD) activity were higher under low O than ambient O or hypoxia. Moreover, the prolonged photoperiod reduced the F/F and Pn among all three O levels but enhanced the Rd, MDA, and SOD activity. Transcriptome data showed that most of 26 differentially expressed genes (DEGs) that mainly relate to photosynthesis, respiration, and metabolism were down-regulated by hypoxia, with varying expression degrees between the 8:16 and 16:8 L:D cycles. In addition, our results demonstrated that the positive or negative effect of lowering O upon the growth of diatoms depends on the O level and is mediated by the photoperiod.
加剧的脱氧现象正在广泛影响海洋生物，浮游植物也不例外。为了探究这些影响，我们在最佳生长光照条件下，比较研究了一种硅藻在不同氧水平和光暗循环条件下的生长、细胞组成、光合作用及转录组。在8:16光暗循环下，低氧使硅藻的生长速率（μ）提高了34%，但缺氧使其降低了22%。然而，在16:8光暗循环下，μ随氧水平降低而下降。在8:16光暗循环下，细胞叶绿素含量随氧水平降低而减少，而在16:8光暗循环下蛋白质含量减少。延长光周期降低了叶绿素含量，但提高了蛋白质含量。在8:16或16:8光暗循环下，低氧降低了最大光系统II光化学量子产率（F/F）、光合放氧速率（Pn）和呼吸速率（Rd）。低氧条件下细胞丙二醛（MDA）含量和超氧化物歧化酶（SOD）活性高于正常氧或缺氧条件。此外，延长光周期在所有三种氧水平下均降低了F/F和Pn，但提高了Rd、MDA和SOD活性。转录组数据显示，26个主要与光合作用、呼吸作用和代谢相关的差异表达基因（DEG）中的大多数在缺氧条件下被下调，在8:16和16:8光暗循环之间下调程度不同。此外，我们的结果表明，降低氧对硅藻生长的正负效应取决于氧水平，并受光周期介导。
