Peroxisomes of the midgut epithelium, malpighian tubules and fat body of larvae of the dragonfly, Aeshna cyanea

The enterocytes of the midgut epithelium of Aeshna cyanea larvae are rich in peroxisomes while the nidal regenerative and endocrine cells contain only a few. Most of the enterocytic peroxisomes are microperoxisomes lacking a crystalloid nucleoid, but peroxisomes with well developed nucleoid are also present. The peroxisomes are usually concentrated in the basal region of the cells but may also spread into the apical region and closely intermingle with absorptive lipid droplets. They significantly increase in number, when the larvae are regularly fed lipid-rich natural food or long-chain monounsaturated fatty acids that are unusual dietary components of these animals. This observation seems to indicate that the enterocytic peroxisomes are involved in chain shortening and degradation of fatty acids absorbed from the gut lumen.Numerous microperoxisomes are also present in the lipid-storing cells of the Malpighian tubules and fat body.     

Cytology of the midgut epithelium of Aeshna larvae (Insecta,Odonata)

Summary The midgut epithelium of the larval dragonfly Aeshna cyanea consists of four types of differentiated cells, which all display secretory activity. Pure secretory cells are the mucocytes and two morphologically distinguishable types of endocrine cells, while the enterocytes exert the dual function of secretion and absorption. Both functions can be performed more or less synchronously; however, appropriate feeding and starvation experiments can stress one function over the other. The heaviest accumulation of secretion granules was observed after a few days of starvation following a long period of regular feeding. Then the enterocytes resembled typical protein-secreting exocrine gland cells. It is still unknown whether the two main secretions, namely digestive enzymes and peritrophic membrane material, are jointly or separately distributed in the secretion granules. The morphological findings suggest that the secretory products follow the same cisternal pathway via endoplasmic reticulum, Golgi apparatus, membrane-bound storage granules and exocytotic extrusion that is well established for the exocrine pancreas of vertebrates. The routes of protein secretion and lipid absorption through the enterocytes of Aeshna are discussed in comparison with the enterocytes and mammocytes of vertebrates.Dedicated to Prof. Dr. K.E. Wohlfarth-Bottermann on the occasion of his 65^th birthday     

Differential absorption and esterification of dietary long‐chain fatty acids by larvae of the dragonfly,Aeshna cyanea

In order to evaluate whether dietary long‐chain fatty acids were differentially absorbed, Aeshna cyanea larvae received 5 μl oral doses containing combinations of two radiolabeled fatty acids at nearly equal radioactive and nmolar concentrations: (1) ³H‐oleic and ¹⁴C‐palmitic acids; (2) ³H‐oleic and ¹⁴C‐stearic acids; and (3) ³H‐palmitic and ¹⁴C‐stearic acids. After 3 h or 1 day, hemolymph samples, midgut tissue, midgut contents and fat body tissue were collected and assayed for labeled fatty acids. The ³H/¹⁴C ratios indicated that there was a preference for absorption of the monounsaturated oleic acid over both saturated palmitic and stearic acids and that the shorter palmitic acid was absorbed at a higher rate than the longer stearic acid. There were also differences in the ³H/¹⁴C ratios of the various lipid classes of the midgut wall, hemolymph, and fat body that reflected differential esterifications and transport of these fatty acids. Arch. Insect Biochem. Physiol. 40:183–193, 1999. © 1999 Wiley‐Liss, Inc.     

Junctional structures in the metamorphosing midgut of Aeshna cyanea (Insecta,Odonata)

Summary The metamorphosing midgut of Aeshna cyanea is characterized by the successive development of two tissues: the reticulated tissue and the imaginal epithelium. These tissues supply information concerning contacts between cells diverging in their developmental pathways although arising from the same stem cell population. In addition to small desmosomes, which bind reticulated to imaginal cells, the reticulated cells form invaginations into the apex of imaginai epithelial cells. The projections of the reticulated cells have enlarged tips, and numerous microfilaments run longitudinally along the length of theses processes. It is suggested that the anchoring projections of these cells delay the casting off of the reticulated tissue into the lumen, and thus allow the development of the imaginal microvilli. These project into the dilated intercellular space filled with a glycoprotein material that separates imaginal and reticulated cells (Andries, 1972).     

The terminal bar in the larval midgut epithelium ofAeshna cyanea

Summary Thin section and freeze-fracture electron microscopy revealed that the terminal bars of the larval midgut epithelium ofAeshna cyanea consisted of extended smooth septate junctions (SSJ), multiple adhesive junctions and rare gap junctions. Freeze-fractures of native tissue suggested that the septal building units were anchored only in the external membrane leaflet by partially integrated proteins while the interseptal pegs were anchored partly in both leaflets by completely integrated proteins and partly by presumed peripheral proteins.Reversible depletion of the physiological Ca⁺⁺ concentration had no apparent structural effect on the SSJ of the terminal bars, but led to a reversible formation of junctional septa between the foot processes concomitant with a rearrangement of IMPs in the basolateral plasma membranes. The basolateral SSJ assembly and disassembly induced by reversible Ca⁺⁺ deprivation was interpreted as exaggerated response of an intrinsic capability normally related to the apical growth of regenerative cells and to the extrusion of degenerating cells. Lanthanum tracer ingested with hyperosmotic drinking solution was always found excluded from the basolateral intercellular spaces underneath the terminal bar, but there was a dual effect on the SSJ structure. Part of the junctions remained structurally intact, part was dissociated in the apical portion and invaded by tracer.Abbreviations EF exoplasmic fracture face - EGTA ethylenglycol-bis(2-aminoethylether)-N,N-tetraacetic acid - IMP intramembrane particle - PAS periodic acid Schiff reagent - PF protoplasmic fracture face - PSJ pleated septate junction - SDS sodium dodecyl sulphate - SSJ smooth septate junction Dedicated to Prof. Dr. E.Scholtyseck in honour of his 65th birthday.     

Specialization of the endoplasmic reticulum in the apex of the midgut cells of Aeshna cyanea (Insecta,Odonata)

Summary Lamellar stacks of cisternae regularly spaced and bound to each other by fine filaments are observed in the apex of midgut cells of Aeshna cyanea. These cisternae are connected with the rough endoplasmic reticulum but are devoid of ribosomes except on their terminal sacs. Their location and their structure, quite different in fed and starved animals, suggest that they are involved in intracellular transport.     

The macrophyte, Stratiotes aloides, protects larvae of dragonfly Aeshna viridis against fish predation

Predation could be one force determining which contemporary species occupy a certain habitat. Aeshna viridis is an endangered dragonfly species with a larval distribution strongly associated with lakes where the water plant, water soldier, Stratiotes aloides, occurs. In this study, the larvae were almost exclusively found in patches of S. aloides. To study larval association with S. aloides further, we conducted a series of laboratory experiments. Behavioural experiments indicated that larvae preferred S. aloides. Aeshna viridis larvae were nocturnal and rather inactive. Larvae on S. aloides were less susceptible to predation by the perch, Perca fluviatilis, than larvae on another water plant, Myriophyllum alterniflorum. According to our study it seems that occurrence of S. aloides may limit the distribution of A. viridis, and the protection of refuges may be essential in planning the conservation of this endangered species.     

Fatty acid composition of fat body and malpighian tubules of the tenebrionid beetle, Zophobas atratus: Significance in eicosanoid-mediated physiology

Total and phospholipid fatty acid composition of fat body and Malpighian tubules from two larval stages, pupae and adults, of Zophobas atratus were analyzed. Saturated and unsaturated C16 and C18 fatty acids were major components and varied by life stage and tissue source. Eicosanoid-precursor fatty acids, including 20:3n-6, 20:4n-6 and 20:5n-3, were present in low quantities and varied by life stage and tissue source. 20:3n-6 was always present in the lowest proportions, indicating that eicosanoids derived from 20:4n-6 and 20:5n-3 (the 2- and 3-series) are likely to be of greater physiological significance in this insect. Fatty acid composition of Z. atratus fat body and Malpighian tubules was independent of diet, suggesting that this insect controls its fatty acid composition to meet the needs of individual tissues and ontogenetic constraints.     

A novel insect defensin mediates the inducible antibacterial activity in larvae of the dragonfly Aeschna cyanea (Paleoptera, Odonata).

The injection of low doses of bacteria into the aquatic larvae of dragonflies (Aeschna cyanea, Odonata, Paleoptera) induces the appearance in their hemolymph of a potent antibacterial activity. We have isolated a 38-residue peptide from this hemolymph which is strongly active against Gram-positive bacteria and also shows activity against one of the Gram-negative bacteria which was tested. The peptide is a novel member of the insect defensin family of inducible antibacterial peptides, which had so far only been reported from the higher insect orders believed to have evolved 100 million years after the Paleoptera. Aeschna defensin is more potent than defensin from the dipteran Phormia, from which its structure differs in several interesting aspects, which are discussed in the paper.     

Toxin-binding proteins from midgut epithelium membranes of Anopheles stephensi larvae

Proteins of 65 and 57 kD were isolated from the apical membranes of midgut epithelium of Anopheles stephensi larvae by affinity chromatography. These proteins can specifically bind endotoxin Cry11A and activate toxin Cry4B (Cry4B-tox) under conditions of ligand blotting, and both Cry proteins compete for this binding. At least in the case of Cry4B-tox, the binding with 65 and 57 kD proteins is reversible. The ability of the products of limited proteolysis of Cry11A and Cry4B to bind the 65 and 57 kD proteins correlates with their toxicity to A. stephensi larva. The N-terminal amino acid sequence of the 57 kD protein is unique and absent in the NCBI GenBank. The proteins of 65 and 57 kD share most of the properties studied with Aedes aegypti toxin-binding proteins. It is possible that they altogether represent a novel class (or classes) of delta-endotoxin receptors.     

Ultrastructure of the malpighian tubules of Schistocerca gregaria

The ultrastructure of the Malpighian tubules of the adult desert locust, Schistocerca gregaria, is described. Male and female adults possess about 233 tubules, which empty proximally into the midgut-ileal region of the alimentary canal by way of 12 ampullae. The tubules vary from 10 mm to 23 mm in length. About one third of them are directed anteriorly, attaching distally at the caeca, while the remainder are directed posteriorly, attaching to other tubules, the rectum or large tracheal trunks adjacent to the hindgut. The Malpighian tubules from all locations examined consist of three ultrastructurally distinct regions: proximal, middle, and distal, referring to their position relative to the midgut. All cell types possess ultrastructural features characteristic of ion transporting tissue, i.e., elaboration of the basal and apical membranes and a close association of these membranes with mitochondria. The distal and proximal segments are short (1.5-1.7 mm) and heavily tracheated, and each is composed of a single, distinct cell type. The middle region is the longest segment of the Malpighian tubule and is composed of two distinct cell types, primary and secondary. Both cell types are binucleate. The more numerous primary cells have large nuclei, contain laminate concretions in membrane-bound vacuoles, and possess large microvilli that contain mitochondria. The secondary cells are smaller and possess smaller nuclei. The microvilli are reduced and lack mitochondria. Secondary cells do not contain laminate concretions. The possible compartmentalization of ion and fluid transport function based on segmentation in the Malpighian tubules is discussed.     

Peroxisomal acyl-CoA oxidase and chain-shortening of dietary fatty acids in the midgut of dragonfly larvae, Aeshna cyanea

Activity of peroxisomal acyl-CoA oxidase was measured in homogenates of Aeshna cyanea midguts and found to be reversibly influenced by long-term fasting and refeeding.

The enzyme was immunocytochemically colocalized with catalase in the peroxisomes of the intestinal absorptive cells.

Orally administered nervonic and erucic acids were present in the triacylglycerol fraction of the midgut epithelium together with chain-shortened intermediates. But they were not detected in the diacylglycerol fraction of the haemolymph and triacylglycerol fraction of the fat body, which only contained chain-shortened intermediates. The prevalence of oleic acid in these three fractions suggests that the very long-chain fatty acids tested are assimilated by chain-shortening on their absorptive-pathway across the midgut epithelium.     

Growth and differentiation of secondary malpighian tubules in the cockroach,Periplaneta americana

Four differentiated Malpighian tubules (primary tubules) extend from the junction of the midgut and hindgut in newly hatched Periplaneta americana. Secondary tubules begin to develop near the base of the primary tubules before hatching and successive nymphal molts. The newly initiated tubules undergo cell division and extensive elongation through the middle of the following intermolt period. During this time, the cells of the distal, middle, and lower middle tubule regions are surrounded by a cellular sheath, have few cytoplasmic processes extending along their basal surfaces, have a small or nonexistent lumen, and contain extremely dilated cisternae of endoplasmic reticulum. The cellular sheath differentiates into the muscle which coils around the mature tubule. Tubules which begin development toward the end of one intermolt period begin to undergo cytodifferentiation toward the end of the next intermolt period. By the middle of an additional intermolt period, the basal infoldings and microvilli of cells in the distal, middle, and lower middle regions have the conformations typical for those regions in differentiated tubules; granular concretions and stellate cells are present within the middle region of the tubule.     

Developmental changes in fat body and midgut chromosomes of Drosophila auraria

Changes in puffing activity of fat body (FB) and midgut (MG) chromosomes of Drosophila auraria during late larval and white prepupal development as well as after in vitro culture with or without ecdysterone were studied and compared with those of the salivary gland (SG). The Balbiani Rings characteristic of the SG chromosomes of D. auraria, are not formed in FB and MG. Most of the inverted tandem chromosomal duplications that have been found to be common to all three tissues showed differentiation of puffing activity of the bands considered to be homologous. The major early ecdysone puffs 73A and 73B (considered to be homologues of D. melanogaster puffs 74EF and 75B, respectively), together with other early ecdysone puffs were present in all three tissues. Clear intermoult and postintermoult puffs were not evident in FB and MG chromosomes. However, a small set of late ecdysone puffs could be scored in FB, while no late ecdysone puffs were abserved in MG. Other tissue-specific puffs were identified, but a very small number of them were limited to MG.by W. Beermann