title: Uric acid spherulites in the reflector layer of firefly light organ.
abstract: BACKGROUND
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors: Institute of Molecular and Cellular Biology, Department of Life Science, National Tsing-Hua University, Hsinchu, Taiwan.
authors: King-Siang
authors: KS
authors: Goh
authors: Hwo-Shuenn
authors: HS
authors: Sheu
authors: Tzu-En
authors: TE
authors: Hua
authors: Mei-Hua
authors: MH
authors: Kang
authors: Chia-Wei
authors: CW
authors: Li
mesh_terms: D000818:Animals; D002412:Cations / Q000378:metabolism; D048888:Fireflies / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D049449:Luminescence; D008297:Male; D009928:Organ Specificity; D014527:Uric Acid / Q000378:metabolism*; D014961:X-Ray Diffraction
chemical_list: D002412:Cations; D014527:Uric Acid