Environmental Engineering Reference
In-Depth Information
2002
; Ashraf and Harris
2004
; Munns
2005
). This osmolyte is also important for
other metabolic functions like regulation of osmo- and redox-systems (Sharma and
Dietz
2006
), stabilization of biological membranes (Matysik et al.
2002
), chelation
of metals (Cobbett
2000
; Sharma and Dietz
2006
), scavenging of reactive oxygen
species (Alia et al.
2001
), and protection of enzymes (Öztürk and Demir
2002
).
A significant increase in the accumulation of proline has been reported by sev-
eral researchers in a number of plant species under metal stress, which is compa-
rable to other abiotic stresses. Schat et al. (
1997
) reported a significant increase in
the proline content in
Silene vulgaris,
which is a metal-sensitive plant. However,
metal-tolerant plants may accumulate high quantities of proline under heavy metal
stress, which is critical in the protection of a plant species from oxidative damage
of biological membranes (Dubey and Pessarakli
2002
; Gratao et al.
2008
). Schat
et al. (
1997
) observed that Cu concentration can induce proline accumulation much
higher than Cd and Zn. Alia and Saradhi (
1991
) and Bassi and Sharma (
1993
) rated
Cu and Cd as strong inducers of proline in many plant species. Accumulation of
proline under toxic levels of Cd has also been reported by several authors in differ-
ent plant species, e.g.,
Vetiveria zizanioides
(Pang et al.
2003
), transgenic plants and
algae (Sharma and Dietz
2006
),
Oryza sativa
(Shah and Dubey
1998
)
Vigna radiata
(Muneer et al.
2011
) and
Brassica juncea
(John et al.
2009
). Overall, like for other
streses, praline accumulation is an important indicator of metal tolerance in most
plant species.
3.2.4
Inorganic Ions
Inorganic ion uptake and translocation, particularly during germination and early
seedling stages, has been reported to be sensitive to high concentration of heavy met-
als (Gabbrielli et al.
1990
; Kovačević et al.
1999
; Pandey and Sharma
2003
; Seregin
and Kozhevnikova
2005
; Hasinur et al.
2005
). There are several reports on metal
toxicity that affect concentrations of Ca, Mg, Zn, Fe, Mn and many other essen-
tial nutrients (Heale and Ormrod
1982
; Marschner
1995
; Nieminen and Helmisaari
1996
; Küpper et al.
1996
). Aziz et al. (
2007
) and Ali et al. (
2009
) reported a reduc-
tion in N, P, K and S contents under nickel toxicity, whereas Palacios et al. (
1998
)
reported a significant reduction in the absorption and translocation of Na
+
. Nickel
(Ni) can also competitively remove Ca
2+
ions from its binding site (Boisvert et al.
2007
) by replacing Mg
2+
, which inhibits the reaction of electron transport during
photosynthesis (Küpper et al.
1998
; Souza and Rauser
2003
; Solymosi et al.
2004
).
This ultimately causes nutrient deficiencies, which can severely affect growth and
development of a plant species (Liu
2008
; Gonçalves et al.
2009
).
Metals like Fe, Cu, Zn and Mn are the primary components of many metaboli-
cally active enzymes (superoxide dismutase, catalase, etc.). Heavy metal toxicity
can lead to reduced biosynthesis of these enzymes (Molas
2002
; Gajewska et al.
2006
). This can significantly suppress vegetative growth, and ultimately the poor
biomass production and yield reduction (Schützendübel and Polle
2002
; Gajewska
and Skłodowska
2007
).