Agriculture Reference
In-Depth Information
in etiolated plants. Moreover, in roots of the transgenic CAT-deficient tobacco lines
(
CAT 1AS
), the DNA damage induced by Cd was higher than in wild type tobacco
(
SR 1
) roots (Gichner et al.
2004
). Furthermore, CAT activity remained unaltered
under Cd stress in
Glycine max
leaves (Ferreira et al.
2002
).
Glutathione reductase (EC 1.6.4.2) is a flavo-protein oxidoreductase, found in
both prokaryotes and eukaryotes (Mullineaux and Rausch
2005
; Romero-puertas
et al.
2006
). This enzyme was first reported in eukaryotes and yeast (Meldrum and
Tarr
1935
) as well as in plants (Conn and Vennesland
1951
; Mapson and Goddord
1951
). Glutathione reductase maintains the balance between reduced glutathione
(GSH) and ascorbate pools, which in turn maintain cellular redox state (Lascano
et al.
1999
2001
; Reddy and Raghavendra
2006
; Romero-Puertas et al.
2006
; An-
sel et al.
2006
; Chalapathi Rao and Reddy
2008
). The enzyme protein, although
synthesized in the cytoplasm, can be targeted to both chloroplast and mitochon-
dria (Mullineaux and Rausch
2005
). In higher plants, GR is involved in defense
against oxidative stress, whereas GSH plays an important role within the cell sys-
tem, which includes participation in the ascorbate-glutathione cycle, maintenance
of the sulphhydryl (-SH) group and a substrate for glutathione-S-transferases (Noc-
tor et al.
2002
; Reddy and Raghavendra
2006
). GR and GSH play a crucial role in
determining the tolerance of a plant during environmental stresses (Chalapathi Rao
and Reddy
2008
). In almost all the biological functions, GSH is oxidized to GSSG
which should be converted back to GSH in plant cell to perform normal physi-
ological functions. Hence, rapid recycling of GSH is more essential rather than
synthesis of GSH, which is a highly regulated and ATP requiring process. GR activ-
ity increases as part of the defense against Cd-exposure, which is dose-dependent
and variable over time (Fornazier et al.
2002a
). The GR activity increased in the
presence of Cd in
Phaseolus vulgaris
(Chaoui et al.
1997a
),
Solanum tuberosum
(Stroinski and Zielezinska
1997
),
Raphanus sativus
(Vitoria et al.
2001
),
Crotolaria
juncea
(Pereira et al.
2002
),
Glycine max
(Ferreira et al.
2002
),
Saccharum offici-
narum
(Fornazier et al.
2002b
),
Capsicum annuum
(Leon et al. 2002),
Arabidopsis
thaliana
(Skorzynska et al.
2003
/2004),
Vigna mungo
(Singh et al.
2008
),
Triti-
cum aestivum
(Khan et al.
2007
) and
Brassica juncea
(Mobin and Khan
2007
). In
Raphanus sativus,
it exhibited very little variation in the roots and leaves of control
plants, indicating a direct correlation with Cd accumulation (Vitoria et al.
2001
).
In
Pisum sativum
, GR activity was enhanced more with 40 μM than with 4 μM Cd
(Dixit et al.
2001
). However, a decrease in GR activity after application of Cd has
also been reported for a few plant species such as
Helianthus annuus
(Gallego et al.
1996a
,
b
),
Pisum sativum
(Dalurzo et al.
1997
) and
Solanum tuberosum
(Stroinski
and Kozlowska
1997
).
Glutathione S-transferases (EC 2.5.1.18) catalyze the conjugation of tripeptide
GSH into a variety of hydrophobic, electrophylic and cytotoxic substrates (Marrs
1996
). Noctor et al. (
2002
) observed that GSTs can remove genotoxic or cytotoxic
compounds that have potential to damage or react with genetic material (DNAs and
RNAs) and protein. In fact, glutathione-S-transferases can reduce peroxides with
the help of GSH and produce scavengers of cytotoxic and genotoxic compounds.
An increased GST activity was found in leaves and roots of Cd-exposed
Pisum sa-
