Searching for biological pigments and structural color in fossil plants

尽管人们对活植物的绚丽色彩研究得很透彻，但对化石植物的绚丽色彩却很少关注。在现存的植物群中，植物的颜色主要是由生物色素产生的，也被称为生物色素，它以大量的色调表达，如绿色、黄色、橙色、红色、粉红色、蓝色、紫色、紫外线、棕褐色、棕色、灰色和白色。植物中的颜色也可以来自结构颜色，或者很少来自生物发光。结构色来自于表面的物理和结构修饰，通过在微纳米尺度上周期性地排列材料，使植物呈现金属蓝色、银色或彩虹色。生物色素和结构色极有可能在很早的时候就存在于植物体内。然而，在植物化石中对色素颜色的研究很少，而在叶或果实化石中对结构颜色的研究尚未见报道。绿色的新生代叶子和明显的粉红色侏罗纪藻类是已知的少数具有色素沉着的化石植物的有趣例子。然而，鉴于今天可用的高度精确和敏感的仪器和方法，应该有可能提取、鉴定和定量植物色素，如叶绿素、类胡萝卜素和花青素及其衍生物。一些具有彩色叶子的新生代植物群为色素研究提供了希望，如美国爱达荷州中新世的Clarkia植物群和德国东部始新世的Geiseltal植物群。虽然叶绿素的衍生物已经从这两种植物的绿色化石叶子中提取和鉴定出来，但其他色素很可能也在沉积后的1500万到4500万年中幸存下来，波恩大学制药研究所新购买的高灵敏度和精确的Sciex QTRAP 6500+系统，三重四极杆/线性离子阱LCMS/MS质谱仪将能够检测和测量。非破坏性的方法，如共聚焦拉曼光谱，将用于颜料的检测、鉴定和化学分析。对于博物馆藏品的实地工作和侦察，还将探索使用手持式光谱仪对具有色素残留的有希望的标本进行初步评估。同样，使用非破坏性的高分辨率方法，如低真空扫描电子显微镜，将被用于寻找化石叶子表面可能产生结构颜色的纳米结构。由于结构色在雨林植物的遮荫叶片中以闪烁的彩虹色最常见，我们将使用波恩大学古生物学部门新获得的高性能变压TESCAN Vega 4扫描电镜分析来自新生代保护lagerstätten的叶子，例如法兰克福附近梅塞尔的热带初新世植物群。

Although the dazzling colors in living plants are well studied, those in fossil plants have received little attention. In the extant flora, plant color is primarily produced by biological pigments, also known as biochromes, which are expressed in a huge array of hues such as green, yellow, orange, red, pink, blue, violet, ultraviolet, tan, brown, gray, and white. Colors in plants can also arise from structural color or, rarely, from bioluminescence. Structural colors come from the physical and structural modification of surfaces through periodically arranged material on the micro- or nanoscale that make plants appear metallic blue, silver, or iridescent. It is highly likely that biochromes and structural color existed in plants in deep time. However, only a handful of cases of pigmentary color have been studied in fossil plants, and examples of structural color in fossil leaves or fruits have not been reported. Green Cenozoic leaves and a distinctly pink-colored Jurassic alga are among the few intriguing examples of fossil plants known to have pigmentation. Yet, given the highly accurate and sensitive instrumentation and methodology available today, it should be possible to extract, identify, and quantify plant pigments such as chlorophylls, carotenoids, and anthocyanins and their derivatives in fossil plants today. Several Cenozoic floras with colored leaves show promise for pigment research, such as the Miocene Clarkia flora in Idaho, USA, and the Eocene Geiseltal flora in eastern Germany. While derivatives of chlorophyll have been extracted and identified from green fossil leaves from both floras, it is likely that other pigments have also survived the 15 to 45 million years since deposition, which the newly purchased, highly sensitive and accurate Sciex QTRAP 6500+ System, a triple quadrupole/linear ion trap LCMS/MS mass spectrometer, in the Pharmaceutical Institute at the University of Bonn will be able to detect and measure. Non-destructive methods, such as confocal Raman spectroscopy, will be developed for the detection, identification, and chemical analysis of pigments. For field work and reconnaissance in museum collections, the non-destructive use of a hand-held spectrometer for the initial evaluation of promising specimens with pigmentary color remains will also be explored. Similarly, the use of a non-destructive, high-resolution approach, such as low-vacuum scanning electron microscopy, will be employed to search for nanostructures on the surface of fossil leaves that may have produced structural color. Because structural color is most common as a shimmery iridescence in the shade leaves of rainforest plants, we will analyze leaves from Cenozoic conservation lagerstätten such as the tropical Eocene flora from Messel near Frankfurt with the newly acquired, high-performance, variable-pressure TESCAN Vega 4 SEM at the Division of Paleontology at the University of Bonn.