Agriculture Reference
In-Depth Information
ules, but the activity decreased with high Cd concentration. The lower APX activ-
ity was also noted in
Cucumis sativus
chloroplasts with increasing Cd concentra-
tion (Zhang et al.
2003
), whereas Cd-induced inhibition of APX activity was also
observed in clonal, hydroponically grown
Populus
×
Canescens
(Schutzendubel
et al.
2002
) and
Helianthus annuus
plants (Gallego et al.
1996a
). APX activity in
Ceratophyllum demersum
showed a very high increase in Cd + Zn treated plants as
compared to Cd or Zn alone, indicating efficient antioxidant and ROS scavenging
activities by Zn against Cd-induced free radicals and oxidative stress (Aravind and
Prasad
2003
). Khan et al. (
2007
) also reported increased APX activity in
Triticum
aestivum
plants treated with Cd under low Zn levels.
Catalase (EC 1.11.1.6) is a heme-containing enzyme that catalyzes the dismuta-
tion of hydrogen peroxide into water and oxygen (Frugoli et al.
1996
). Present in all
aerobic eukaryotes, this is important in the removal of hydrogen peroxide generated
in peroxisomes (microbodies) by oxidases involved in β-oxidation of fatty acids,
the glyoxylate cycle (photorespiration) and purine catabolism. CAT is one of the
first enzymes isolated in a highly purified state. The isozymes of catalase have been
studied extensively in higher plants (Polidoros and Scandalios
1999
). Scandalios
et al. (
2000
) characterized three genetically-distinct CAT isozymes in maize plants.
All forms of the enzyme are tetramers in excess of 220,000 molecular weight.
Multiple forms of catalase have been described in many plants. Maize has three
isoforms termed as
CAT 1
,
CAT 2
and
CAT 3
, which are found on separate chro-
mosomes and are differentially expressed and independently regulated (Scandalios
1990
).
CAT 1
and
CAT 2
are localised in peroxisomes and the cytosol, whereas CAT
3 is mitochondrial. Plants contain multiple CAT isozymes, e.g., 2 in
Hordeum vul-
gare
(Azevedo et al.
1998
), 4 in
Helianthus annuus
cotyledons (Azpilicueta et al.
2007
) and as many as 12 isozymes in mustard (Frugoli et al.
1996
). CAT isozymes
have been shown to be regulated temporally and spatially and may respond differ-
entially to light (Willekens et al.
1994
, Skadsen et al.
1995
).
The variable response of CAT activity has been observed under Cd stress. CAT
activity declined in
Helianthus annuus
leaves (Gallego et al.
1996b
),
Phaseolus
vulgaris
(Chaoui et al.
1997b
),
Phaseolus aureus
(Shaw
1995
),
Pisum sativum
(Dalurzo et al.
1997
),
Lemna minor
(Mohan and Hossetti
1997
),
Amaranthus livi-
dus
(Bhattacharjee
1998
),
Glycine max
roots (Balestrasse et al.
2001
),
Phragmites
australis
(Iannelli et al.
2002
),
Capsicum annuum
(Leon et al. 2002) and
Arabidop-
sis thaliana
(Cho and Seo 2005) under Cd stress conditions. A significant decline
in CAT activity was reported after 50 µM Cd applications for 48 hr in the roots and
shoots of
Bacopa monnieri
(Singh et al.
2006
). However, CAT activity increased in
Agropyronrepens
(Brej
1998
),
Helianthus annus
(Gallego et al.
1999
),
Glycine max
nodules (Balestrasse et al.
2001
),
Oryza sativa
leaves (Hsu and Kao
2004
), in toler-
ant varieties of
Solanum tuberosum
(Stroinski and Kozlowska
1997
), in roots of
Raphanus sativus
seedlings (Vitoria et al.
2001
),
Brassica juncea
(Mobin and Khan
2007
),
Triticum aestivum
(Khan et al.
2007
),
Vigna mungo
roots (Singh et al.
2008
)
and
Cicer arietinum
(Hasan et al.
2008
). Azpilicueta et al. (
2007
) reported that incu-
bation of
Helianthus annuus
leaf discs with 300 and 500 µM CdCl
2
under light con-
ditions increased
CATA3
transcript level but this transcript was not induced by Cd
