Spermatogenesis in "Pteridophytes": Ultrastructure Differentiation and Phylogeny

早期生命形式第一次成功地从水中迁移到陆地上是所有生物事件中最重要和最令人困惑的事件之一。大约5亿年前，生活在沼泽里的藻类上岸，为动植物的繁盛奠定了基础。然而，人们仍然不确定这种祖先的藻类是什么样子的，以及今天存在的各种植物群与这种假定的祖先之间的关系，以及彼此之间的关系。本项目旨在通过对无籽维管束植物翼蕨的精子细胞发育和结构的研究来解决这些基本问题。蕨类植物包括蕨类、棒状藓、穗状藓、刺草和马尾草。现代蕨类植物的精子细胞为古代陆地植物的功能、结构和进化提供了线索。游动的精子是当代植物中唯一的活动细胞，因此它们带有水生藻类祖先的特征。追踪它们的分化和结构为早期陆生植物谱系提供了线索，并将最终确定一直追溯到祖先藻类的进化线索。十种被认为精子细胞与最早的陆生生物最相似的翼生动物将成为电子显微镜检查的目标。每株植物将拍摄500多张详细的显微照片。将对这些照片进行分析，并制作三维图像来描绘发展的各个阶段。此外，计算机将跟踪和分析大约100种细胞特征的信息，从细胞形状到蛋白质成分。重点将放在检查参与组织这些高度复杂的运动细胞的结构实体的蛋白质的作用。研究结果将有助于在植物世界复杂的谱系树上更准确地定位这十个信息丰富的物种。这些分析还将更清楚地解决哪些现代藻类是陆生植物的近亲，以及在陆地植物生命的早期历史中原始植物群的出现顺序。除此之外，这些研究还提供了更多关于所有生命形式中细胞的组织、分化和进化的基本信息。

9527735 RENZAGLIA The first successful migration of early life forms from water to land was one of the most significant and perplexing of all biological events. Nearly 500 million years ago, swamp-dwelling algae made it ashore and thus set the stage for the magnificent flourish of plants and animals to come. Yet, it is still uncertain as to what this ancestral alga looked like and how the diverse plant groups that exist today are related to this presumed ancestor, and to each other. This project proposes to address these fundamental questions by examining sperm cell development and structure in a critical group of seedless vascular plants, the OpteridophytesO. Plants included among the OpteridophytesO include ferns, club mosses, spike mosses, quillworts, and horsetails. Sperm cells in modern OpteridophytesO hold clues to the functioning, structure and evolution of ancient land plants. Swimming sperm are the only motile cells of contemporary plants and as such they carry traits of their aquatic algal ancestors. Tracing their differentiation and architecture provides clues to early land plant lineages and will eventually identify evolutionary threads leading all the way back to the ancestral algae. Ten OpteridophytesO, species whose sperm cells are thought to resemble most closely those of the first terrestrial organisms, will be targeted for electron microscopic examination. More than 500 detailed micrographs will be taken for each plant. These photographs will be analyzed and three-dimensional images will be prepared to depict the stages of development. In addition, computers will track and analyze information on approximately 100 cell traits, from cell shape to protein components. Emphasis will be placed on examining the role of proteins that are involved in organizing the structural entities of these highly complicated motile cells. The results will help place these ten informative species more correctly on the plant worldOs complex genealogical tree. These analyses will also more clearly resolve which modern algae are the closest relatives to terrestrial plants and the sequence of appearance of the primitive plant groups during the early history of plant life on land. Beyond that, these studies provide more essential information about the organization, differentiation and evolution of cells in all forms of life.