The single-celled green alga Dunaliella salina is a model system for studies on stress biology, in particular regarding secondary carotenoid accumulation. Under non-stress conditions the cells are green, but under abiotic stress the cells turn orange, because they switch their metabolism and accumulate β-Carotene in globules in the chloroplast. For the first time, Quick-freeze deep-etch electron microscopy was used to visualize cellular structures in green and orange cells of D. salina strain CCAP19/18. This allowed us to present an in-depth analysis of the cellular ultrastructure describing and comparing the features of the two cell types. Our images illustrate the presence of a pericellular matrix for this strain of D. salina. The pericellular matrix was spongy and strands of unknown material anchored it into the plasma membrane. The cytoplasm contained a variety of vesicles, vacuoles, and acidocalcisomes. We could show for strain CCAP19/18 that cytoplasmic lipid bodies were often in close proximity to and sometimes in contact with the outer chloroplast envelope membrane and with the endoplasmic reticulum. Major visible differences between green and orange cells were in the chloroplast: the orange cells have greatly reduced amounts of thylakoid membranes and greatly increased numbers of β-Carotene globules. We showed that the β-Carotene globules often made point contacts with thylakoid membranes, and frequently laid side-by-side along the thylakoid membrane surface, providing support to studies that indicated exchange of molecules between β-Carotene globules and thylakoid membranes. A novel finding was the β-Carotene globule duplets, suggesting intermediate stages in β-Carotene globule morphogenesis. Overall, the β-Carotene globules appear to be similar to plant plastoglobuli. We provide this description of the cellular ultrastructure features as a resource in the context of the recent publication of the genome of D. salina strain CCAP19/18 to expand on the knowledge regarding this novel reference strain.

单细胞绿藻杜氏盐藻是用于应激生物学研究的模型系统，特别是关于次级类胡萝卜素积累的模型。在非胁迫条件下，细胞为绿色，但在非生物胁迫下，细胞变为橙色，因为它们会改变其代谢并在叶绿体中的小球中积累β-胡萝卜素。首次使用快速冷冻深蚀刻电子显微镜观察了盐藻D. salina菌株CCAP19 / 18的绿色和橙色细胞中的细胞结构。这使我们能够对细胞超微结构进行深入分析，以描述和比较两种细胞类型的特征。我们的图像说明了该盐藻D. salina菌株存在细胞周围基质。细胞周围基质呈海绵状，未知材料束将其锚定在质膜中。细胞质包含各种囊泡，液泡和酸性钙酶异构体。对于菌株CCAP19 / 18，我们可以证明细胞质脂质体通常与叶绿体外膜和内质网非常接近，有时甚至接触。绿色和橙色细胞之间的主要可见差异在于叶绿体：橙色细胞的类囊体膜量大大减少，β-胡萝卜素小球数量大大增加。我们发现，β-胡萝卜素球经常与类囊体膜进行点接​​触，并经常沿类囊体膜表面并排放置，为表明β-胡萝卜素小球和类囊体膜之间分子交换的研究提供支持。β-胡萝卜素小球团是一个新发现，表明β-胡萝卜素小球形态发生处于中间阶段。总体而言，β-胡萝卜素小球似乎与植物质体球相似。我们提供细胞超微结构特征的这种描述作为资源的最新出版物的背景下。盐藻D. salina菌株CCAP19 / 18扩展了有关该新型参考菌株的知识。