Biomedical Engineering Reference
In-Depth Information
(Hu et al. 2009). The observed tolerance, in most cases, was attributed to
the elevated levels of antioxidant system (Yu et al. 2003, Azevedo-Neto et
al. 2005). Transgenic plants with reduced catalase activity (and therefore
presumed increased endogenous H
2
O
2
concentrations) showed elevated
defense gene expression and cell necrosis in high light intensities where
AOS would be generated (Chamnongpol et al. 1996).
An alternative approach to the manipulation of endogenous
concentrations of H
2
O
2
is the expression of heterologous glucose oxidase
(
GOX
) genes in plants (Wu et al. 1995). Leaves of transgenic potato plants
containing a chimeric
GOX
gene of
Aspergillus niger
with expression
driven by the caulifl ower mosaic virus (CaMV) 35S promoter had H
2
O
2
concentrations two- to threefold higher than those of non-transgenic controls
and were also more resistant to infections by
P. infestans
. Similarly, this
gene was also used to enhance the tolerance of potato, tobacco, cotton and
rice against some of their dreadful pathogens (Wu et al. 1995, Murray et
al. 1999, Kachroo et al. 2003) and the observed resistance or tolerance was
attributed to HR response (Kazan et al. 1998) and induction of pathogenesis-
related (PR) proteins (Kachroo et al. 2003). Moreover, it was observed that
the pathogen inducible expression of
GOX
results in timely accumulation
of H
2
O
2
, which is suffi cient to confer enhanced resistance to the rice blast
pathogen
Magnaporthe grisea
in contrast to the constitutive expression of
GOX
that causes many developmental abnormalities (Kachroo et al. 2003).
However, effects of expression of this
GOX
gene on plant cell viability and
the induction of defense genes were not reported in this previous study. In a
research undertaken by Kazan et al. (1998), they tested whether expression
of a heterologous
GOX
gene in transgenic plants has the potential to activate
cell death and induce plant defense genes. The
GOX
gene was derived from
the fungus
Talaromyces fl avus
and was expressed in transgenic tobacco and
canola in a construct where expression was driven by a peroxidase gene
promoter that is weakly expressed constitutively but is highly responsive
to infection by fungal pathogens and wounding (Curtis et al. 1997). They
envisaged that this gene would permit an assessment of the potential of
GOX
as a tool for engineering hypersensitivity and defense gene induction
in transgenic plants. The results indicate that
GOX
expression can induce
cell death and defense gene induction and this effect of the transgene is
further potentiated by exogenous SA. However, with this gene construct,
the effi cacy of
GOX
expression for generating plant cell death and activating
defense genes appears to be limited by glucose supply in the plant (Kazan
et al. 1998).
Interestingly enhanced
GOX
expression can also confer resistance
to plants for withstanding abiotic stress along with biotic stresses.
Maruthasalam et al. (2010) enhanced the endogenous H
2
O
2
content of
tobacco plants by the constitutive expression of a
GOX
gene of
Aspergillus
