Agriculture Reference
In-Depth Information
In diplopods, the fat body, both parietal and perivisceral, is constituted of trophocytes and
oenocytes (Fontanetti et al., 2004) and presents intense metabolic activity, such as storage of
lipids, uric acid and proteins as well as storage, neutralization and excretion of substances
that are not useful (Fontanetti et al., 2006; Hopkin & Head, 1992; Hubert, 1979). In this
sense, Souza et al. (2011) exposed diplopods of the species
R. padbergi
in bioassays
containing industrial soil contaminated by PAHs and metals (landfarming) in order to
analyze histological and histochemical alterations in the perivisceral fat body. The authors
concluded that the fat body can be used as a target organ and that the alterations observed,
such as loss of integrity of the plasmatic membrane, cytoplasmic disorganization and
depletion of energetic reserves can be considered stress biomarkers in this animal. Similar
responses were observed in animals exposed to sewage sludge (Abe et al., 2010).
4.2 Genotoxicity biomarkers
The increase in the genotoxic load in the terrestrial ecosystems by the release of chemical
products and physical agents can cause impact on the organisms, inducing increase in the
frequency of mutations; such effects can lead to a decrease in the size of the population and,
eventually, extinction of species and consequently affect the stability of this ecosystem
(Majer et al., 2005). In this sense, it became necessary to develop different tests to evaluate
the genotoxic potential of soil samples.
Due to the highly conserved structure of the genetic material, it is possible to use a wide
variety of species in genotoxicity tests; currently, the most widespread methods for the
routine tests are based on the use of indicator bacteria and also basidiomycetes fungi, plants,
insects and cultured mammalian cells or even laboratory animals for mutagenicity tests.
According to the literature, the Ames test is the most widely used in genotoxicity
evaluations of soils and leachate (Claxton et al., 2010; Wölz et al., 2011). This test, also
known as
Salmonella/
microsome, consists, basically, in the employment of strains of the
auxotrophic bacteria
Salmonella typhimurium
, i.e., deficient in the synthesis of the aminoacid
histidine; the strains of these cells are unable to grow in minimum medium, where the
mutagenic compounds are able to restore the synthesis capacity of this aminoacid, thus, the
mutagenic expression corresponds to the growth of the colony in a minimum culture
medium and it can be easily detected by counting the colonies (Umbuzeiro & Vargas, 2003).
However, due to the low sensitivity of the Ames test for heavy metals, more studies should
be directed to the development of bioassays with higher organisms (Gatehouse et al., 1990,
as cited in Lah et al., 2008).
Meristematic cells of
A. cepa
and
V. faba
, for example, constitute an effective cytogenetic
material to analyze chromosome aberrations (figure 6) caused by soil pollution. The use of
meristematic cells makes possible the quantification of several morphological and
cytogenetic parameters (endpoints), including the morphology and growth of roots and
determination of several parameters of cytotoxicity, genotoxicity and mutagenicity. The
analysis of the cytotoxicity can be done by determining the mitotic index and cell death. The
induction of aberrant metaphases, anaphases and telophases, such as bridges, loss and
chromosome stickiness, polyploidy, irregular nuclei and nuclear buds are parameters for
the genotoxicity analysis, while the micronuclei and chromosome breaks allow the
mutagenicity analysis (Fernandes et al., 2007; Leme & Marin-Morales, 2008; Souza et al.,
2009).
Chromosome aberration test concerns the discovery of the mechanisms of action of a
particular agent, since the division process is well known. Kovalchuk et al
.
(1998) state that
