Ferritin in iron containing granules from the fat body of the honeybees Apis mellifera and Scaptotrigona postica

It is already known that the behaviour of the honeybee Apis mellifera is in fluenced by the Earth's magnetic field. Recently it has been proposed that iron-rich granules found inside the fat body cells of this honeybee had sma ll magnetite crystals that were responsible for this behaviour. In the pres ent work, we studied the iron containing granules from queens of two specie s of honeybees (A. mellifera and Scaptotrigona postica) by electron microsc opy methods in order to clarify this point. The granules were found inside rough endoplasmic reticulum cisternae. Energy dispersive X-ray analysis of granules from A. mellifera showed the presence of iron, phosphorus and calc ium. The same analysis performed on the granules of S. postica also indicat ed the presence of these elements along with the additional element magnesi um. The granules of A. mellifera were composed of apoferritin-like particle s in the periphery while in the core, clusters of organised particles resem bling holoferritin were seen. The larger and more mineralised granules of S . postica presented structures resembling ferritin cores in the periphery, and smaller electron dense particles inside the bulk. Electron spectroscopi c images of the granules from A. mellifera showed that iron, oxygen and pho sphorus were co-localised in the ferritin-like deposits. These results indi cate that the iron-rich granules of these honeybees are formed by accumulat ion of ferritin and its degraded forms together with elements present insid e the rough endoplasmic reticulum, such as phosphorus, calcium and magnesiu m. It is suggested that the high level of phosphate in the milieu would pre vent the crystallisation of iron oxides in these structures, making very un likely their participation in magnetoreception mechanisms. They are most pr obably involved in iron homeostasis. (C) 2001 Elsevier Science Ltd. All rig hts reserved.