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 ).
Search WWH ::




Custom Search