Effects of Photoperiods on the Pigment Composition in Marine Diatom Phaeodactylum tricornutum

Diatoms are crucial photoautotrophic phytoplankton, playing a vital role in marine ecosystems due to their efficient photosynthesis and ability to adapt to fluctuating light environments. The light adaptation of diatoms is primarily regulated by pigments, which not only form light-harvesting complexes but also participate in photoprotective mechanisms. Light-dark (LD) cycles are key environmental factors regulating diatom physiology. In recent years, the antioxidant, UV-protective, and anti-inflammatory properties of diatom pigments have been increasingly recognized, highlighting their growing application value. Understanding how diatoms regulate pigment biosynthesis under different LD cycles is crucial for both theoretical and applied research. In this study, the model diatom Phaeodactylum tricornutum was used to investigate the regulation of pigment synthesis under different LD cycles (LD 24:0, LD 16:8, LD 12:12, LD 8:16, LD 4:2, LD 2:2, and LD 2:4). Physiological responses, including growth rate, pigment composition, photosynthetic parameters, and elemental composition, were assessed alongside transcriptomic analysis. The results demonstrated that intermittent light enhanced growth rate to some extent, with peak pigment content observed under the LD 2:2 condition. Additionally, intermittent light increased the ratio of photosynthetic to photoprotective pigments while reducing the de-epoxidation level of diadinoxanthin. Pigment composition exhibited phase-specific variations: chlorophyll a dominated in the exponential phase, while fucoxanthin increased in the stationary phase. Photosynthetic parameters indicated higher efficiency under intermittent light, while the LD 24:0 group exhibited the lowest values. Transcriptomic analysis revealed that moderate-length LD cycles (LD 2:2 and LD 12:12) significantly upregulated genes involved in carotenoid biosynthesis, chlorophyll biosynthesis, and light-harvesting complex proteins. This study offers theoretical support for understanding diatom light adaptation strategies and their application research.硅藻是一类关键的光合自养型浮游植物，凭借高效的光合作用能力与适应波动光环境的特性，在海洋生态系统中发挥着至关重要的作用。硅藻的光适应过程主要由色素调控，这些色素不仅可构成光捕获复合物（light-harvesting complexes），还参与光保护机制（photoprotective mechanisms）。光暗周期（Light-dark cycles, LD）是调控硅藻生理过程的核心环境因素。近年来，硅藻色素的抗氧化、抗紫外线与抗炎活性日益受到学界关注，凸显出其愈发可观的应用价值。解析硅藻在不同光暗周期下调控色素生物合成的机制，无论对理论研究还是应用研究均具有重要意义。本研究以模式硅藻三角褐指藻（Phaeodactylum tricornutum）为研究对象，探究了不同光暗周期（LD 24:0、LD 16:8、LD 12:12、LD 8:16、LD 4:2、LD 2:2及LD 2:4）下的色素合成调控机制。研究同步测定了生长速率、色素组成、光合参数及元素组成等生理响应指标，并开展了转录组分析（transcriptomic analysis）。研究结果显示，间歇性光照在一定程度上提升了生长速率，且在LD 2:2光暗周期下色素含量达到峰值。此外，间歇性光照提高了光合色素与光保护色素的比值，同时降低了硅藻黄质（diadinoxanthin）的脱环氧化水平。色素组成呈现出阶段特异性变化：叶绿素a（chlorophyll a）在指数生长期占主导地位，而岩藻黄素（fucoxanthin）在稳定期含量显著升高。光合参数结果表明，间歇性光照下的光合效率更高，而LD 24:0组的光合效率最低。转录组分析显示，中等时长的光暗周期（LD 2:2与LD 12:12）可显著上调参与类胡萝卜素生物合成（carotenoid biosynthesis）、叶绿素生物合成（chlorophyll biosynthesis）及光捕获复合物蛋白的相关基因。本研究为解析硅藻的光适应策略及其应用研究提供了坚实的理论支撑。