Minio Miles, Battistuzzi Mariano, Norici Alessandra, La Rocca Nicoletta, Pagliano Cristina, Gerotto Caterina
Department of Life and Environmental Sciences, Università Politecnica Delle Marche, Ancona, Italy.
Department of Biology, University of Padova, Padova, Italy.
Physiol Plant. 2025 Jul-Aug;177(4):e70401. doi: 10.1111/ppl.70401.
Sulfur (S) is an essential macroelement for photosynthetic organisms and is acquired as sulfate and assimilated as sulfide into cysteine through a highly demanding reductive process. S is a key component of proteins, lipids, and various other cellular metabolites and plays a direct role in photosynthesis, both in the electron transport and in carbon fixation reactions. Despite such central functions, most of our knowledge on S metabolism is focused on plant species, while in microalgae it is still fragmented, particularly concerning their huge phylogenetic diversity. Here, we investigated responses to continuous low sulfate availability in three marine microalgae, two Chlorophytes, Tetraselmis suecica and Dunaliella salina, and the diatom Phaeodactylum tricornutum, by characterizing their growth, photosynthesis, elemental, and macromolecular composition. As a general trend, all the microalgae acclimated to the low sulfate medium prioritized the allocation of available resources to photosynthesis. By modulating their pigment content per cell and the stoichiometry of their photosynthetic apparatus, S-limited cells kept in vivo photosynthetic activity close to that of control cultures. Conversely, growth and cell composition were modulated in a species-specific manner. Results are discussed also in an evolutionary perspective, taking into consideration that, throughout Earth's history, sulfate concentration significantly increased from ancient to modern oceans, and such variation was paralleled by changes in the ecological abundances between algal groups, with the red algae lineage of present-day oceans supplanting the green algae, more abundant in the past.
硫（S）是光合生物必需的大量元素，以硫酸盐形式获取，并通过一个高需求的还原过程以硫化物形式同化为半胱氨酸。硫是蛋白质、脂质和各种其他细胞代谢物的关键组成部分，在光合作用的电子传递和碳固定反应中都发挥着直接作用。尽管有这些核心功能，但我们对硫代谢的了解大多集中在植物物种上，而在微藻中，相关知识仍然零散，尤其是考虑到它们巨大的系统发育多样性。在这里，我们通过表征三种海洋微藻（两种绿藻，即瑞典四爿藻和盐生杜氏藻，以及硅藻三角褐指藻）的生长、光合作用、元素和大分子组成，研究了它们对持续低硫酸盐可用性的响应。总体趋势是，所有适应低硫酸盐培养基的微藻都优先将可用资源分配到光合作用中。通过调节每个细胞的色素含量和光合装置的化学计量，硫限制细胞的体内光合活性接近对照培养物。相反，生长和细胞组成则以物种特异性方式进行调节。我们还从进化的角度讨论了结果，考虑到在地球历史上，硫酸盐浓度从古海洋到现代海洋显著增加，这种变化与藻类群体之间生态丰度的变化并行，当今海洋中的红藻谱系取代了过去更为丰富的绿藻。
