Environmental Engineering Reference
In-Depth Information
protein, and proline; increased malondialdehyde
(MDA) content; and elevated metal uptake were
ameliorated by applications of 28-HBL. In addi-
tion, the activities of all the antioxidant enzymes
except guaiacol peroxidase (POD), increased
significantly when subjected to Cr stress in com-
bination with 28-HBL. Overall, seed presoaking
treatment of 28-HBL at 10
− 7
M was most effec-
tive in ameliorating Cr stress.
Gangwar et al.
2011
). Furthermore, Gangwar
et al. (2011) also studied effects of exogenous
GA (10 and 100 μM) application on growth, pro-
tein and nitrogen contents, ammonium (NH
4+
)
content, enzymes of nitrogen assimilation, and
antioxidant system in pea seedlings under Cr(VI)
phytotoxicity. They showed that exogenous ap-
plication of GA led to different changes in pea
seedlings, that Cr and 100 ﾵM GA alone as well
as in combination decreased growth and altered
nitrogen assimilation in pea seedlings compared
to control, which was attributed to decreased
levels of antioxidants. In contrast, application of
10 ﾵM GA together with Cr was able to alleviate
Cr phytotoxicity appreciably. This 10 ﾵM GA-
mediated amelioration of Cr phytotoxicity was
assigned to the better antioxidant system and sus-
tained activities of enzymes of nitrogen assimila-
tion. Therefore, it is suggested that GA may play
different roles based on its exogenous concentra-
tions and plant species used under specific devel-
opmental and environmental conditions.
3. Kinetin application
Heavy metals have been reported to reduce the
contents of cytokinins probably as a result of
hormone breakdown or by enhancing the activ-
ity of cytokinin oxidase (Kaminek et al.
1997
).
Hence, exogenous application of kinetin to al-
leviate the deleterious effects of heavy metal
toxicity in plants is gaining importance (Hussain
et al.
2007
). Hussain et al. further studied the
role of kinetin in alleviating the toxic effects of
Pb and Cr on four black gram cultivars com-
monly cultivated in Pakistan. In the roots of one
line (Mash ES1), they reported relatively higher
concentration of both metals as compared to its
shoot, suggesting its importance for phytoreme-
diation, while in another line (Mash 80), heavy
metal content was lower in both shoot and roots
suggesting its utilization in future breeding pro-
grams and cultivation as a fodder crop in the riv-
erine areas of Pakistan and other places which are
prone to excessive heavy metal contamination,
particularly Pb and Cr (Hussain et al.
2007
).
6.2.2
Glutathione Application for
Amelioration of Chromium
Phytotoxicity
GSH is a tripeptide detected virtually in all cell
compartments such as cytosol, chloroplast, en-
doplasmic reticulum, vacuole, and mitochondria.
The chemical reactivity of the thiol group of GSH
makes it particularly suitable to serve a broad
range of biochemical functions in all organisms,
and it is one of the major sources of nonprotein
thiols in most plant cells. The nucleophilic nature
of the thiol group is also important in the forma-
tion of mercaptide bonds with metals and for re-
acting with selected electrophiles. This reactivity
along with the relative stability and high water
solubility of GSH makes it an ideal biochemical
to protect plants against stresses including oxida-
tive stress, heavy metals, and certain exogenous
and endogenous organic chemicals (Millar et al.
2003
; Foyer and Noctor
2005
; Rausch et al.
2007
; Yadav
2010
). Reduced GSH acts as an an-
tioxidant and is involved directly in the reduc-
tion of most ROS generated during stress (Millar
4. Gibberellic acid application
Gibberellic acid (GA) is one of the key plant
hormones influencing seed germination, stem
elongation, leaf expansion, and reproductive
development (Hooley
1994
; Matsuoka
2003
).
Studies have shown that exogenous application
of GA provides protection to plants against abi-
otic stresses and increases crop yield (Tuna et al.
2008
; Wen et al.
2010
). However, excess appli-
cations of GA have shown to increase ethylene
production, ROS generation, and alterations in
defense mechanisms of plants, causing tissue
damage and retarded growth (Celik et al.
2007
;
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