Shaked Noy, Sorrentino Andrea, Varsano Neta, Addadi Sefi, Porat Ziv, Pinkas Iddo, Weiner Steve, Addadi Lia
Department of Chemical and Structural Biology, Weizmann Institute of Science, Rehovot, Israel.
MISTRAL Beamline, Experiments Division, ALBA Synchrotron Light Source, Cerdanyola del Valles, Barcelona, Spain.
PLoS One. 2025 Feb 12;20(2):e0316193. doi: 10.1371/journal.pone.0316193. eCollection 2025.
Organic crystals, and in particular guanine crystals, are widely used by multicellular organisms for manipulating light and producing structural colors. Many single celled eukaryotic organisms also produce organic crystals, and guanine is the most abundant type produced. Their functions are thought to be related to the fact that guanine is nitrogen rich. Here we studied a freshwater unicellular eukaryotic alga, Phacotus lenticularis, and found that when the growth medium is depleted in phosphorus, the alga stops reproducing and produces intracellular birefringent particles inside vesicles. Cryo-SEM showed that these particles are faceted and are located within membranes inside the cell. Using Raman spectroscopy, we showed that these particles are β-guanine crystals. 3D tomograms produced using cryo-soft-X-ray-microscopy quantitatively documented the increase in cell volume and distribution of guanine crystals within the cells with increasing time of phosphorous deprivation. The tomograms also showed additional morphological changes in other cellular organelles, namely starch granules, chloroplasts, nuclear DNA and membranes. The combined observations all indicate that under phosphorous depletion, the algal cells undergo a massive stress response. As guanine crystal formation is part of this response, we conclude that guanine crystals are formed in response to stress, and this is not related to nitrogen availability. Upon addition of phosphate to the P-depleted media, the algal cells, with their guanine crystals, resume reproduction. From this we conclude that the guanine crystals somehow contribute to the recovery from stress.
有机晶体，尤其是鸟嘌呤晶体，被多细胞生物广泛用于操控光线和产生结构色。许多单细胞真核生物也会产生有机晶体，其中鸟嘌呤是产生最多的类型。人们认为它们的功能与鸟嘌呤富含氮这一事实有关。在这里，我们研究了一种淡水单细胞真核藻类——透镜鼓藻，并发现当生长培养基中的磷耗尽时，这种藻类会停止繁殖，并在囊泡内产生细胞内双折射颗粒。冷冻扫描电子显微镜显示这些颗粒有小平面，位于细胞内的膜内。利用拉曼光谱，我们表明这些颗粒是β-鸟嘌呤晶体。使用冷冻软X射线显微镜产生的三维断层扫描定量记录了随着磷缺乏时间的增加，细胞体积的增加以及鸟嘌呤晶体在细胞内的分布。断层扫描还显示了其他细胞器，即淀粉颗粒、叶绿体、核DNA和膜的额外形态变化。综合观察结果都表明，在磷缺乏的情况下，藻类细胞会经历大规模的应激反应。由于鸟嘌呤晶体的形成是这种反应的一部分，我们得出结论，鸟嘌呤晶体是在应激反应中形成的，这与氮的可用性无关。向缺磷培养基中添加磷酸盐后，带有鸟嘌呤晶体的藻类细胞恢复繁殖。由此我们得出结论，鸟嘌呤晶体以某种方式有助于从应激中恢复。
