Application of analytical electron microscopic methods to investigate the function of spherites in the midgut of the larval antlion Euroleon nostras (Neuroptera: Myrmeleontidae)

Abstract

This study presents an application of analytical electron microscopy in biology to investigate the chemical composition of the spherites and to elucidate the importance of these methods in the life sciences. The structure of the spherites in the midgut cells of first, second, and third instar larvae Euroleon nostras was investigated by a combination of transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDXS), electron energy-loss spectroscopy (EELS), and energy filtering TEM (EFTEM). The structure and chemical composition of the spherites changed during the metamorphosis. In first larvae, the spherites are composed of amorphous, flocculent material, containing C, N, and O. In second larvae and third ones, the spherites have concentric layers of alternating electron-dense and electron-lucent material. In second larvae, Si, P, Ca, and Fe are accumulated in the spherite organic matrix, composed of C, N, and O. In the spherites of third larvae, additionally Al was found. Therefore, the spherites are thought to store organic compounds in all three larval stages of E. nostras and additionally inorganic compounds in second and third ones. In first larvae, spherites are present in the midgut cells; in second and third larvae, they are present in the cells of the midgut and in its lumen. It could be suggested that the spherites might be involved in the regulation of the appropriate mineral composition of the internal environment and could serve as the accumulation site of nontoxic waste materials that cannot be metabolized.

Honey Bees (Apis mellifera, L.) as Active Samplers of Airborne Particulate Matter

“…Interestingly, the honey bees from both the Sardinian polluted area and the control site carried spherites characterized by the same chemical elements (C, Ca, K, Mg, Mn, N, Na, O, P, S, Zn), as already reported in other insect species [ 43 – 45 ].…”

“…The ventriculum and Malpighian tubules of the bees from both Sardinian and control sites showed a conspicuous number of spherocrystals (spherites), as commonly found in many insect species, where it has been demonstrated that they originates from the endoplasmic reticulum–Golgi complex [ 43 , 44 ]. The function of these granules, mainly composed by phosphates and/or urates, may be related to ionic and homeostatic regulation, but they also seem to serve as storage sites of essential inorganic compounds, and even toxic waste materials as heavy metals [ 44 , 45 ].…”

Structural and functional alterations in Malpighian tubules as biomarkers of environmental pollution: synopsis and prospective

“…Detoxification mechanisms at cellular level include the accumulation of metal‐binding proteins (e.g. metallothioneins; Dallinger, ) and the precipitation of metals as intracellular electron‐dense granules (Köhler, ; Lipovšek Delakorda et al, ) or spherites (Ballan‐Dufrançais, ; Lipovšek et al, ; Talarico et al, ). X‐ray microanalysis performed on ultrathin sections of Malpighian tubules has shown that spherites and granules are composed of a set of metals (see Ballan‐Dufrançais, , for a complete review of analysed species).…”

Ultrastructural analysis of apoptosis and autophagy in the midgut epithelium of Piscicola geometra (Annelida, Hirudinida) after blood feeding

“…Therefore, several mechanisms which neutralize the toxic molecules must be activated in order to maintain the homeostasis of the organism (Okuda et al 2005 , 2007 ). Toxic substances can accumulate in numerous structures called spherites (Oliveira et al 2000 ; Lipovšek et al 2002 , 2012 ) or in vacuoles called endosomes (Tarnowski and Coons 1989). The perimicrovillar or the peritrophic membranes, which separate the midgut epithelium from the midgut lumen, protect the organism against the entrance of pathogens or toxic substances (Terra 2001 ; Albuquerque-Cunha et al 2004 ; Terra and Ferreira 2012 ).…”