Elsevier

Micron

Volume 37, Issue 7, October 2006, Pages 648-656
Micron

Fat body of Prorhinotermes simplex (Isoptera: Rhinotermitidae): Ultrastructure, inter-caste differences and lipid composition

https://doi.org/10.1016/j.micron.2006.01.012Get rights and content

Abstract

Ultrastructure of the fat body was studied in following castes and developmental stages of Prorhinotermes simplex: larvae of the first and the second instar, pseudergates, presoldiers, soldiers, nymphs, imagoes and mature ergatoid neotenic reproductives of both sexes. Fat body always consists of two principal cell types: adipocytes and urocytes. Adipocytes are characterized by a presence of large amounts of storage substances, namely lipid droplets, glycogen rosettes and proteins in the form of either biocrystals or vacuoles. Proportion of these components strongly varies during ontogeny. Adipocytes are equipped by a large central vacuole in which lipid droplets may resolve. Cytoplasm of urocytes contain glycogen rosettes and spherical or irregular concretions, other organelles are rare. Only adipocytes change their inner structure in the course of ontogeny: amount of glycogen decreases during the postembryonic development, it is the major kind of inclusion in the larvae but lacks in nymphs and imagoes; opposite trend is performed by lipids. The changes in protein content are less obvious but are explained and discussed. The total amount of triacylglycerols (TAGs) was found to be roughly 100 μg in a pseudergate, 250 μg in a nymph, and 30 μg in a soldier. The most abundant fatty acids in TAGs are oleic (O), stearic (S), palmitic (P) and linoleic (L) acid. TAGs form a complex mixture with OOO, OPO, OLO and OOS being the most abundant isomers. Only negligible differences exist among the castes.

Introduction

The fat body of insects is a very important organ concerned especially with storage of nutrients and intermediary metabolism (Keeley, 1985, Haunerland and Shirk, 1995, Chapman, 1998). For those reasons, it has been studied in many insect groups (for a review see Dean et al., 1985, Keeley, 1985, Locke, 1998). The structure of the fat body remains relatively uniform and many similar features occur in non-relative species.

Generally, the fat body is a ribbon-like tissue formed by adipocytes, but other cell types (urocytes, mycetocytes, oenocytes belong to more frequent ones) may occur as well (Dean et al., 1985, Haunerland and Shirk, 1995, Chapman, 1998). Adipocytes are characterized by a presence of lipid droplets (droplets of triacylglycerols), glycogen rosettes and protein granules (Dean et al., 1985, Haunerland and Shirk, 1995, Chapman, 1998, Locke, 1998, Canavoso et al., 2001). Urocytes contain predominantly spherical concretions made by uric acid (Haunerland and Shirk, 1995, Chapman, 1998). Termite fat body consists of adipocytes and urocytes (Grassé, 1982, Han and Bordereau, 1982a, Han and Bordereau, 1982b). Other cell types (mycetocytes, oenocytes) were observed rarely, only in a single species (Grassé, 1982, Sacchi et al., 2000).

The postembryonic development of termites comprise several castes with clear specialization to fill particular tasks: soldiers are intended for colony defence, reproductives for breeding, workers (temporary workers = pseudergates in the genus Prorhinotermes) for food processing and taking care for the dependent castes. Therefore important differences in intermediary metabolism are expected among particular castes and variation in the fat body structure is expected to occur due to these differences. The aim of this paper is to compare the fat body structure in the fundamental castes and developmental stages throughout the whole ontogeny of the model species, Prorhinotermes simplex, and to resume the changes in content of major storage inclusions.

Section snippets

Termites

All individuals of Prorhinotermes simplex (Hagen, 1858) originated from a colony collected by Dr. J. Křeček in Soroa (Piñar del Rio, Cuba) in 1964 and since that time kept in laboratory at 26 ± 1 °C. Studied specimens were removed from the colony and promptly fixed in the period from December, 1998, to November, 2001. For ontogenetical pathways occurring in the genus Prorhinotermes see Roisin (1988).

TEM sample preparation

We used larvae in the stage of the first and the second instar, pseudergates, presoldiers,

Common characters of the fat body cells

Fat body of P. simplex consists of two principal cell types: adipocytes (Fig. 1) and urocytes (Fig. 5). Both types are present in all castes and developmental stages. Adipocytes and urocytes are interfused; in cross section through a single fat body ribbon, the urocyte is placed centrally and surrounded by four to six adipocytes. Adipocytes are usually about 30 μm in the largest dimension (rarely up to 40 μm, but in larvae never exceeding 25 μm). The fat body ribbons are enclosed in basement

Discussion

The general development of the fat body well corresponds with the previous observations. Basic features of adipocytes and urocytes are similar to other termite and cockroach species (Gharagozlou, 1965, Han and Bordereau, 1982a, Han and Bordereau, 1982b, Grassé, 1982, Hyatt and Marshall, 1985, Polver et al., 1986). Oenocytes and mycetocytes are lacking in the fat body of P. simplex in contrary to some termite species (Grassé, 1982, Sacchi et al., 2000).

The results on ultrastructure of so-called

Acknowledgement

The authors wish to thank to the staff of Laboratory of Electron Microscopy (Institute of Parasitology, Czech Academy of Sciences), to Jitka Pflegerová (Laboratory of Digital Imaging in Entomology, Institute of Entomology, Czech Academy of Sciences) for their valuable help during sample preparation, and to Karel Stránský (Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences) for GC analysis. Jan Šobotník, Robert Hanus and Josef Cvačka thank to Z4 055 0506 project realized

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