Studies On Ultrastructure Of Light Organs Of Two Aquatic Fireflies

The research of firefly in mainland China breaks the ice just now. With regard to thefirefly light organs, abroad research are around mainly the emergence of light, controlmechamism and light organ ultrastructure of terrestrial fireflies and so on. The authorstudied the ultrastructure of light organs of the two aquatic fireflies to discuss the differenceof light organs between the two rare aquatic fireflies——LucioIa substriata and Luciola leiifound in Wuhan and provide basis to high efficiency of fireflies′bioluminescence.The adult firefly light organs of L. substriata was simple. They were consisted of twoconspicuous layers——the reflecting layer and the photogenic layer. The ventral adult lightorgans segments were in turn composed of body cuticle, the reflecting layer, the photogeniclayer and the interior cell layer from the outside. The reflecting layer which was suppliedwith evolved trachea was composed of compact urate vesicules, and the layer was reflexibleto light; the photogenic layer which emitted their light by the biochemical reaction inphotocyte cytoplasm was composed of mass of photocytes containing typical photocytegranules, mitochondria, endoplasmic reticulum and a rich supply of glycogen. The twolayers ofL. substriata were both covered with acellular membrane, and the distance betweenthe two layers was 25～30μm. The microstructure of adult firefly light organs of L. leiiwere both consisted of two layers——the reflecting layer and the photogenic layer. Thereflecting layer was composed of compact urate vesicules, and had strong tracheals whichcan provide enough oxygen for adult light organs. The trachea had tracheal epithelium. Thephotogenic layer was composed of photocytes. Photocyte granules were generally orbicularand dispersed in cytoplasm. Mitochondria distributed mainly where closed to the photocytesmembrane. There were evolved trachea which were similar to the trachea in the reflectinglayer between the reflecting layer and the inner cell layer.The larval firefly light organs of L. substriata and L. leii were complicated. The larvallight organ of L. substriata was elliptic, covered with acellular layer and consisted with thedorsal layer and photogenic layer. The dorsal layer consisted of a single tier of columnarcells which contained many urate vesicules. Photocytes'membrane interlocked each other.Photocytes contained two types of photocyte granules: one was compact, the other was inapoptosis. The photogenic layer contained numerous mitochondria and amorphous granules.Numerous tracheaes, tracheoles and nerve endings ran between photocytes. The synapsescan be observed. The larval light organ of L. leii which covered with acellular layer wasorbicular, and its diameter was 0.38±0.035 mm (n=30). The larval light organ did notconsisted of two conspicuous layers. The larval light organ contained large empty and transparent structures at its edge and both consisted of numerous photocytes whichcontained many typical photocyte granules. The tertiary tracheae entered the light organ andthere were 2-4 muscles crossing the larval light organ. The muscles can fix the light organ.The larval light organ of L. leii contained numerous tracheae and tracheoles. There werelarge nerves that connected with the larval light organ. The difference of the distancebetween this two larval light organ was significant.Differences between the larval and adult light organs of the two aquatic fireflieswere: the photocyte granules of the adult firefly light organs lied to the middle of thephotocytes, but in the larval firefly light organs that dispersed in the cytoplasm; the larvallight organs had direct innervations, but the adult light organs had not; the mitochondria inadult photocytes distributed mainly where closed to the photocytes membrane, but themitochondria in larval photocytes lied in photocytes; the adult light organs were consisted oftwo layers——the reflecting layer and photogenic layer, but the larval light organ of L. leiihad transparent structures in the border of the larval light organ and were not consisted oftwo layers. The similarities of the larval and adult light organs of the two aquatic fireflieswere: the mechanism of bioluminescence was same; the photocyte granules were similar;both had evolved tracheaes.Compared with the two rare aquatic fireflies, the terrestrial adult fireflies reflectinglayer and photogenic layer were not covered with acellular membrane, and the two layershad not conspicuous separation. The photocyte granules were not in regular shape,and thenumber of tracheoles coming off each tracheal twig was definitely two. The terrestrial larvalfireflies photogenic layer were very different in shape and the dorsal layer were composedof a single tier of cells or two to four tiers of cells.The similarities of L. substriata andterrestrial fireflies were: adult light organ both consisted of the reflecting layer andphotogenic layer; photocytes both contained photocyte granules, mitochondria and a lot ofglycogen; light organ both supplied with evolved tracheaes; photocyte granules were verysimilar. And larval light organ both were composed of the dorsal layer and photogenic layer,and had evolved tracheae and direct innervation. They also had analogical photocytegranules and both were covered with acellular layer.