Plastid Sequestration in Mesodinium rubrum: Physiological, Molecular, and Ecological Aspects

红色中观虫是海洋浮游生物中的一种单细胞成员，可以形成广泛的赤潮。它的不同寻常之处在于，尽管它是一种“原生动物”(类似动物的细胞)，但它含有大量的叶绿体(进行光合作用的细胞器)，可以利用阳光中的能量从二氧化碳和水中制造自己的食物，因此它是类似植物的。尽管红色中观虫似乎是通过摄取藻类来获得其质体，但它只需要偶尔捕食藻类，而且这些质体似乎能够合成叶绿素，这是光合作用中用来捕捉光线的主要色素。它还暂时藏匿着藻类的细胞核。由于其不同寻常的属性，它可能是一些藻类群体的祖先如何获得光合细胞器的模型。其目的是描述红色中观虫与其捕食藻类的关系，并确定光合作用和生长是否依赖于从藻类中获得新的叶绿体或细胞核和/或依赖于猎物作为食物的消化。另一个目标是确定红色中观虫是否永久地藏匿着藻类细胞器或基因。这些问题将通过对养殖的红色中观虫和浮游生物中的自然种群的实验研究相结合来解决。将结合显微技术、化学技术和同位素技术来研究红色中观虫的生理生态。分子技术将被用来测量红色中观虫中藻类基因的含量和表达，并确定红色中观虫不同种群与其叶绿体之间的关系。这些平行的生理和分子研究将阐明原生动物从藻类中摄取细胞器在细胞进化中的可能作用。

Mesodinium rubrum is a one-celled member of the marine plankton that can form extensive red-tides. It is unusual in that although it is a "Protozoa" (animal-like cell) it contains numerous chloroplasts (the organelles in which photosynthesis occurs) and can make its own food from carbon dioxide and water using the energy in sunlight, and thus is plant-like. Although Mesodinium rubrum appears to derive its plastids from ingestion of algae, it only occasionally requires algal prey and the plastids appear to be capable of synthesizing chlorophyll, the primary pigment used to capture light in photosynthesis. It also temporarily harbors nuclei of algae. Because of its unusual attributes, it may be a model for how ancestors of some algal groups acquired their photosynthetic organelles. The objectives are to describe the relationship of Mesodinium rubrum to its algal prey and to determine if photosynthesis and growth depend on acquisition of new chloroplasts or nuclei from algae and/or on digestion of prey as food. Another goal is to determine if Mesodinium rubrum permanently harbors algal organelles or genes. These questions will be approached using a combination of experimental studies of cultured Mesodinium rubrum and of natural populations in the plankton. A combination of microscopic, chemical, and isotopic techniques will be used to study the physiological ecology of Mesodinium rubrum. Molecular techniques will be used to measure algal gene content and expression in Mesodinium rubrum and to determine relationships among different populations of Mesodinium rubrum and their plastids. These parallel physiological and molecular investigations will elucidate the possible role of organelle uptake from algae by protozoa in cellular evolution.