Department of Structural Biology, Weizmann Institute of Science, 76100 Rehovot, Israel; Bioanalytical Chemistry, Technical University Dresden, 01062 Dresden, Germany.
Department of Chemical Research Support, Weizmann Institute of Science, 76100 Rehovot, Israel.
J Struct Biol. 2019 Jul 1;207(1):12-20. doi: 10.1016/j.jsb.2019.04.009. Epub 2019 Apr 13.
Guanine crystals are used by certain animals, including vertebrates, to produce structural colors or to enhance vision, because of their distinctive reflective properties. Here we use cryo-SEM, cryo- FIB SEM and Raman spectroscopic imaging to characterize crystalline inclusions in a single celled photosynthesizing marine dinoflagellate species. We demonstrate spectroscopically that these inclusions are blocky crystals of anhydrous guanine in the β-polymorph. Two-dimensional cryo-SEM and three-dimensional cryo-FIB-SEM serial block face imaging show that the deposits of anhydrous guanine crystals are closely associated with the chloroplasts. We suggest that the crystalline deposits scatter light either to enhance light exploitation by the chloroplasts, or possibly for protection from UV radiation. This is consistent with the crystal locations within the cell, their shapes and their sizes. As the dinoflagellates are extremely abundant in the oceans and are a major group of photosynthesizing marine organisms, the presence of guanine crystals in this marine organism may have broad significance.
嘌呤晶体被某些动物（包括脊椎动物）用于产生结构色或增强视觉，因为它们具有独特的反射特性。在这里，我们使用冷冻扫描电子显微镜、冷冻聚焦离子束扫描电子显微镜和拉曼光谱成像技术来描述单细胞光合作用海洋甲藻物种中的结晶内含物。我们通过光谱学证明这些内含物是无水嘌呤的块状晶体，呈β-多晶型。二维冷冻扫描电子显微镜和三维冷冻聚焦离子束扫描电子显微镜系列块面成像显示，无水嘌呤晶体的沉积物与叶绿体密切相关。我们认为，结晶沉积物散射光线，要么是为了增强叶绿体的光利用，要么可能是为了防止紫外线辐射。这与细胞内的晶体位置、形状和大小一致。由于甲藻在海洋中极为丰富，并且是主要的光合作用海洋生物群体之一，因此这种海洋生物中存在嘌呤晶体可能具有广泛的意义。
