Agriculture Reference
In-Depth Information
of ROS generates oxidative stress and can cause membrane lipid peroxidation, inac-
tivation of enzymes containing SH groups, and RNA and DNA damage. ROS, par-
ticularly the superoxide radical (O
2
-
) and hydrogen peroxide (H
2
O
2
), are generated
in the cytoplasm, chloroplasts, mitochondria, peroxisomes, and apoplast.
In microorganisms, particularly AMF, the components of antioxidant systems
are not well known. It is known, however, that enzymes such as catalase, peroxi-
dise, and superoxide dismutase participate in the decomposition of ROS. Histori-
cally, research has shown that the establishment of mycorrhizal associations result
in increased plant tolerance to adverse environmental factors, although many of the
effects are attributed to enhanced plant nutrition associated with the AMF. The in-
creased activity and induction of new isoenzymes that participate in the antioxidant
system in mycorrhizal plants confers tolerance to excess superoxide radicals gen-
erated during the prevalence of stress conditions (Costa
2003
). In arbuscular my-
corrhizal associations (
Trifolium pratense
-
G. mosseae
), there is an increase in the
activity and synthesis of new SOD isoenzymes induced through symbiosis (Palma
et al.
1993
).
Through the involvement of oxidative stress enzymes against oxidative dam-
age caused by the increased production of ROS during stress conditions, AMF can
increase the capacity to resist oxidative and environmental stresses in the plant,
conferring increased tolerance to ROS, although the role of these enzymes in my-
corrhizae is little elucidated.
Arbuscular Mycorrhizal Fungi in Plants Tolerance
to Nematode Attacks
The protection of plants against abiotic stress caused by pathogens in soil can also
be attributed to AMF (Moraes et al.
2004
; Meira
2004
; Hol and Cook
2005
; Elsen
et al.
2008
; Meira-Haddad
2008
; Vos et al.
2012
).
AMF can be considered to be biocontrol agents (Azcón-Aguilar and Barea
1996
;
Pozo et al.
2002
) and have received much attention for promoting resistance and/
or tolerance, decreasing the incidence and severity of plant diseases, and reducing
the number of soil pathogens (Cordier et al.
1998
; Hol and Cook
2005
; Borges et al.
2007
; Meira-Haddad
2008
; Vos et al.
2012
).
According to Azcón-Aguilar and Barea (
1996
), AMF promotes the following
mechanisms for biological control of plant diseases: improving the nutritional status
of the host plant, compensation for damage caused by the pathogen, competition for
the site of infection and colonisation site, anatomical and morphological changes in
the root system of the host, changes in the microbial population of the rhizosphere,
and activation of systemic and localised defence mechanisms (Pozo et al.
2002
).
Several studies have demonstrated that AMF affect the reproduction of nema-
todes by reducing oviposition, the number of individuals in the roots of infected
plants, and the number of galls and by increasing plant tolerance to pathogen attack
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