Dissertation Research: The Geological History of Polyploidy in Woody Angiosperms

多倍体，一个生物体中具有多于 两套完整的染色体，是一个共同的和重要的 开花植物（被子植物）的进化现象，但 多倍体历史发展知之甚少。 许多 被子植物染色体基数问题 （对于确定多倍性的程度很重要）和 多倍体的起源可以解决，如果化石植物可以 用于确定其历史。 常见的物理效应之一 多倍体的一个重要特征是细胞体积和大小的普遍增加， 保卫细胞，即控制开口的叶表皮细胞 以及植物的气体交换孔或气孔的关闭。 在 至少有两个先前的研究使用了保护小区测量， 估计红杉和水杉化石分类群的倍性水平。 菲尔德博物馆的古植物学家彼得起重机博士和 芝加哥大学将指导研究生简 Masterson分析了四种木本植物多倍体的历史， 被子植物科：悬铃木科（悬铃木），木兰科， 胡桃科（胡桃）和樟科（月桂）。 这些组 之所以选择它们，是因为它们都有（1）化石遗迹的长期记录;（2） 保存完好的叶角质层样品，具有可测量的保卫细胞， 不同的生长阶段;（3）多倍性水平目前 已知的活物种;和（4）之间的正相关性 基于初步研究的细胞大小和倍性水平，包括 染色体中DNA含量的测定 显微分光光度法 这项工作将确立 多倍体在几个被子植物科和限制 可能促进多倍体的古生态条件。 它 将为围绕基础的辩论提供经验数据， 开花植物的染色体数目，并提供第一次测试 在植物中，假设进化的反向关系， 多样化（一个谱系中的物种数量）和基因组大小 （染色体数目和DNA量）。

Polyploidy, the condition in an organism of having more than two complete sets of chromosomes, is a common and important evolutionary phenomenon in flowering plants (angiosperms), but the historical development of polyploidy is poorly understood. Many questions about the base chromosome number of angiosperms (important for establishing the extent of polyploidy) and the origin of polyploidy could be addressed if fossil plants could be used to determine its history. One of the common physical effects of polyploidy is a general increase in cell volume and in the size of guard cells, the leaf epidermal cells that control the opening and closing of the gas exchange pores or stomates of plants. At least two previous studies have used guard cell measurements to estimate ploidy levels in fossil taxa of Sequoia and Metasequoia. The paleobotanist Dr. Peter Crane of the Field Museum and University of Chicago will supervise graduate student Jane Masterson in an analysis of the history of polyploidy in four woody angiosperm families: Platanaceae (sycamores), Magnoliaceae, Juglandaceae (walnuts), and Lauraceae (laurels). These groups were chosen because all have (1) a long record of fossil remains; (2) well preserved leaf cuticle samples with measurable guard cells at a variety of growth stages; (3) multiple ploidy levels presently known for living species; and (4) a positive correlation between cell size and ploidy level based on preliminary study, including measurement of DNA content in chromosomes using microspectrophotometry. The work will establish the antiquity of polyploidy in several angiosperm families and circumscribe the paleoecological conditions that may have promoted polyploidy. It will contribute empirical data to the debate surrounding the base chromosome number of flowering plants, and provide the first test in plants of the hypothesized inverse relation between evolutionary diversification (numbers of species in a lineage) and genome size (numbers of chromosomes and DNA amounts).