Shedding synchrotron light on the fossil record of early plant evolution

同步加速器揭示早期植物进化的化石记录

• 批准号: NE/J012610/1
• 负责人: Philip Donoghue
• 金额: $ 6.5万
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2012
• 资助国家: 英国
• 起止时间: 2012 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FJ012610%2F1
• 关键词: Shedding; synchrotron; light; fossil; record

The evolution of land plants transformed the surface, atmosphere and ocean of our planet - by fixing carbon through biosynthesis and increased rates of weathering, as well as through establishing a terrestrial environment habitable by animals. Our understanding of how this was brought about rests less on primitive living plants (mosses, liverworts and hornworts) whose evolutionary relationships are poorly understood but, rather, from the microscopic fossil remains of the earliest plants. Two fossilization mechanisms have provided us with unique insights: (i) the snapshot of a hot vent community in the Late Devonian Rhynie Chert where the neighboring plants were enveloped and preserved in minerals from the hot fluids, and (ii) the charcoalification of plants by wildfires in a number of much older deposits through the Silurian and Devonian. The process of charcoalification is instant fossilization - it makes plant material chemically inert and physically brittle but resistant to bacterial decay and preserves anatomical structure to the cellular level - making fossils preserved in this way an unparalleled archive in of plant evolutionary history. Ancient charcolified remains of primitive land plants hold insights into their anatomy to the cellular level, but unlocking this information is very difficult. This invaluable material has traditionally been studied by destructively dissection, yielding glimpses of the internal anatomy along cracks that open up in chance orientations. The overall anatomy has to be pieced together by destroying many specimens and the linkage between internal structures are inferential; many structures are never revealed at all. The obvious alternative is to use non-invasive computed tomography - CT scanning. We introduced a very high resolution method in 2007 of studying charcolified remains of advanced seed and flowering plants using a synchrotron - a kind of particle accelerator. However, the results of analyses of the most ancient land plant remains were terrible - crystals of pyrite (fools gold) have grown within the cell spaces of the fossil remains and the huge difference x-ray absorption between the pyrite (high absorption and scattering) and the charcoal (extremely low absorption) making it impossible to make out any anatomical structure. Since 2007 there have been improvements in the synchrotron beamline measurement technology, but also in the processing of the data that it collects. In particular, the stage in which the raw measurements are converted to x-ray slices, has been improved with filtering algorithms that allow us to see the anatomy of the fossil in pin-sharp detail. Our project will entail optimising the measurement parameters and of algorithms involved in the data processing stages, through collaboration with our long-standing Project Partner Prof Marco Stampanoni at the Swiss Light Source Synchrotron - who build the instruments and program the algorithms for data processing. We will exploit these advances in CT scanning new material of early plant remains that we will recover from the critical fossil deposit in Shropshire. We have extensive experience of computer modelling of fossils from synchrotron data and we will analyse computer models of the fossils, dissecting them virtually to better understand the anatomy and physiology of these early plants, in intimate collaboration with the world expert in the biology of these organisms, Prof Dianne Edwards FRS. This work will allow us to understand the sequence of evolutionary steps in early land plant evolution and, in turn, this work will contribute to our understanding of how land plants transformed the planet, and may also prove pivotal in resolving controversy concerning the evolutionary relationships of their living relatives.

土地植物的演变通过生物合成和风化速率固定碳，以及建立动物可居住的陆地环境，从而改变了我们地球的地面，大气和海洋。我们对如何带来的理解较少，基于原始生物（苔藓，利弗沃特和霍恩沃尔特）的进化关系知之甚少，但从最早的植物的微观化石剩下来看。两种化石机制为我们提供了独特的见解：（i）在泥盆纪晚期的Rhynie Chert中的热气沟社区的快照，在那里，邻近的植物被热液包裹并保存在矿物质中，（ii）植物通过旧金人和德氏二氧化硅的野生植物的炭化化。炭化的过程是即时化石 - 它使植物材料化学惰性和物理上脆性，但对细菌衰减具有抗性，并将解剖结构保留到细胞水平上 - 使化石以这种方式保存为植物进化史的无与伦比的档案。原始土地植物的古老型肉体遗骸对其解剖结构至细胞水平具有洞察力，但是解锁此信息非常困难。传统上，通过破坏性的解剖来研究这种宝贵的材料，从而沿着偶然取向开放的裂缝瞥见了内部解剖结构。必须通过破坏许多标本来拼凑整个解剖结构，并且内部结构之间的联系是推断的。许多结构根本没有揭示。明显的选择是使用非侵入性计算机断层扫描-CT扫描。我们在2007年推出了一种非常高的分辨率方法，该方法是使用同步加速器（一种粒子加速器）研究晚期和开花植物的炭化遗迹。但是，对最古老的土地植物的分析结果令人震惊 - 黄铁矿的晶体（傻瓜）在化石的细胞空间中存在增长，并且在黄铁矿（高吸收和散射）和木炭（极低的吸收）之间X射线吸收的巨大差异使得无法使任何解剖结构变得不可能。自2007年以来，同步器光束线测量技术有所改善，而且在收集的数据的处理过程中也有所改善。特别是，通过过滤算法改善了将原始测量转换为X射线切片的阶段，使我们能够以销售细节看到化石的解剖结构。我们的项目将需要优化数据处理阶段中涉及的测量参数和算法，并通过与我们长期的项目合作伙伴Marco Stampanoni教授在瑞士光源同步器上合作 - 构建仪器并计划数据处理算法。我们将在CT扫描早期植物的新材料中利用这些进步，我们将从什罗普郡的关键化石沉积物中恢复。我们拥有从同步加速器数据中对化石进行计算机建模的丰富经验，我们将分析化石的计算机模型，几乎可以解剖它们，以更好地了解这些早期植物的解剖结构和生理学，并与这些生物体生物学的世界专家进行亲密合作，Dianne Edwards Frs教授。这项工作将使我们能够理解早期土地植物进化中进化步骤的顺序，反过来，这项工作将有助于我们对土地植物如何改变地球的理解，并且也可能证明在解决有关其生物亲戚进化关系的争议方面可能是关键的。

项目成果

The timescale of early land plant evolution.

• DOI: 10.1073/pnas.1719588115
• 发表时间: 2018-03-06
• 期刊: Proceedings of the National Academy of Sciences of the United States of America
• 影响因子: 11.1
• 作者: Morris JL;Puttick MN;Clark JW;Edwards D;Kenrick P;Pressel S;Wellman CH;Yang Z;Schneider H;Donoghue PCJ
• 通讯作者: Donoghue PCJ