Agriculture Reference
In-Depth Information
For such analysis, histology and ultrastructure are used. By these techniques it is possible to
diagnose cellular and sub-cellular symptoms resulted from intoxication as well as locate
symptoms of cellular death and reveal reactions in response to chronic and sub-lethal
exposure in cells and tissues (Fontanetti et al., 2010; Kammenga et al., 2000).
Studies show that one of the main contaminants of the soil, metals, are selectively
concentrated in only one or few organs, or in specific regions of the tissues in most of soil
invertebrates and typically these organs are part of the digestive tract (Dallinger, 1993). For
example, in millipeds (Köhler & Alberti, 1992), isopods (Dallinger & Prosi 1988) and
springtails (Pawert et al., 1996), the epithelium of the midgut is the main target of metals.
Thus, the epithelium of the digestive tract represents the first barrier against the intoxication
of the whole organism (Walker, 1976).
In diplopods, some studies with this approach were performed using the digestive tube and
the fat body (Hopkin et al., 1985; Köhler & Triebskorn, 1998; Triebskorn et al., 1999).
Morphological alterations observed in the midgut (figure 4) and in the perivisceral fat body
(figure 5) of the diplopod
R. padbergi
were successfully used as sublethal biomarkers in the
evaluation of soils contaminated with complex substances such as sewage sludge (Godoy &
Fontanetti, 2010; Nogarol & Fontanetti, 2010, 2011; Perez & Fontanetti, 2011a) and
landfarming (Souza & Fontanetti, 2011; Souza et al., 2011).
In the studies performed with the diplopod
R. padbergi
, it was possible to observe tissular
and cellular responses related to detoxification mechanisms such as increased cytoplasmic
granules (spherocrystals) and intense release of secretory vesicles into the intestinal lumen
of these invertebrates (Nogarol & Fontanetti, 2010; Perez & Fontanetti, 2011a). These
secretory vesicles of the apocrine type seems to help in the detoxification of toxic substances
initially absorbed by the organism and form a protector layer that would reduce the contact
between the toxic agent and the intestinal epithelium.
The formation of agglomerates of haemocytes through the cells of the “fat body” layer was
also observed and this response is directly related to a defence mechanism of the animal.
According to van de Braak (2002), haemocytes can migrate to the injury site in the tissue by
a chemotaxis process that results in inflammation. By this inflammatory reaction, these cells
act in the removal of toxins and possibly help in the re-absorption of the damaged
epithelium in order to maintain the homeostasis of the organism. In a recent review
conducted by Perez and Fontanetti (2011b) it becomes clear that this tissular response is
common in different invertebrates exposed to environmental stress conditions. According to
the authors, the monitoring of the number of haemocytes can be used as a measure of stress
in sentinel species due to environmental contamination.
The mechanisms of defence and detoxification require high and continuous energy
expenditure, especially when the organism is exposed to a toxic agent for a long period. In
this sense, histological and ultrastructural studies showed some of the main responses of
this invertebrate related to higher energetic needs. Nogarol and Fontanetti (2011) observed
at an ultrastructural level a high increase in the number of tracheioles between the cells of
the “fat body” layer that compose the midgut of diplopods sub-chronically exposed to
sewage sludge. The authors suggest that a higher oxygenation of the tissue was necessary to
enable the formation of molecules of adenosine triphosphate (ATP), used in the
detoxification mechanisms.
Toxic agents may be able to cause cellular death by necrosis, evidenced mainly by the
intense cytoplasmic vacuolization in the principal cells of the midgut epithelium of
diplopods exposed to landfarming (Souza & Fontanetti, 2011) and sewage sludge (Nogarol
& Fontanetti, 2011; Perez & Fontanetti, 2011a). In addition to the cytoplasm, other cellular
