Institute of Molecular and Cellular Biology, Department of Life Science, National Tsing-Hua University, Hsinchu, Taiwan.
PLoS One. 2013;8(2):e56406. doi: 10.1371/journal.pone.0056406. Epub 2013 Feb 18.
In firefly light organs, reflector layer is a specialized tissue which is believed to play a key role for increasing the bioluminescence intensity through reflection. However, the nature of this unique tissue remains elusive. In this report, we investigated the role, fine structure and nature of the reflector layer in the light organ of adult Luciola cerata.
Our results indicated that the reflector layer is capable of reflecting bioluminescence, and contains abundant uric acid. Electron microscopy (EM) demonstrated that the cytosol of the reflector layer's cells is filled with densely packed spherical granules, which should be the uric acid granules. These granules are highly regular in size (∼700 nm in diameter), and exhibit a radial internal structure. X-ray diffraction (XRD) analyses revealed that an intense single peak pattern with a d-spacing value of 0.320 nm is specifically detected in the light organ, and is highly similar to the diffraction peak pattern and d-spacing value of needle-formed crystals of monosodium urate monohydrate. However, the molar ratio evaluation of uric acid to various cations (K(+), Na(+), Ca(2+) and Mg(2+)) in the light organ deduced that only a few uric acid molecules were in the form of urate salts. Thus, non-salt uric acid should be the source of the diffraction signal detected in the light organ.
In the light organ, the intense single peak diffraction signal might come from a unique needle-like uric acid form, which is different from other known structures of non-salt uric acid form. The finding of a radial structure in the granules of reflector layer implies that the spherical uric acid granules might be formed by the radial arrangement of needle-formed packing matter.
在萤火虫的发光器官中，反射层是一种特殊的组织，被认为通过反射在提高生物发光强度方面起着关键作用。然而，这种独特组织的性质仍然难以捉摸。在本报告中，我们研究了成年 Ceratolucilia cerata 发光器官中反射层的作用、精细结构和性质。
我们的结果表明，反射层能够反射生物发光，并含有丰富的尿酸。电子显微镜（EM）表明，反射层细胞的细胞质充满了密集排列的球形颗粒，这些颗粒应该是尿酸颗粒。这些颗粒大小非常规则（直径约 700nm），呈现出放射状的内部结构。X 射线衍射（XRD）分析表明，在发光器官中特异性检测到具有 0.320nm 间距值的强烈单一峰图案，与单水合尿酸单钠的针状晶体的衍射峰图案和间距值高度相似。然而，发光器官中尿酸与各种阳离子（K(+)、Na(+)、Ca(2+)和 Mg(2+)）的摩尔比评估表明，只有少数尿酸分子以尿酸盐的形式存在。因此，检测到的发光器官中的衍射信号应该是非盐形式的尿酸。
在发光器官中，强烈的单一峰衍射信号可能来自于独特的针状尿酸形式，与其他已知的非盐尿酸形式不同。反射层颗粒中放射状结构的发现表明，球形尿酸颗粒可能是由针状包装物质的放射状排列形成的。
