Environmental Engineering Reference
In-Depth Information
3.2.3
Organic Osmolytes
Soluble Proteins
Regulation of the metabolism of biomolecules is a reliable selection criterion for the
tolerance of a particular plant species to withstand any type of environmental stress.
Synthesis, concentration and activities of proteins (and nucleic acids) along with
the activities of their metabolizing enzymes are of special interest for plant physi-
ologists (Syros et al.
2005
). Any limitation in the activity of enzymes like RNAase
and protease may affect protein synthesis, which is very critical for germinating
seeds that can significantly affect seed germination (Booker
2004
; Maheshwari and
Dubey
2008
).
Toxic effects of heavy metals, were reported on protein contents in
Brassica
oleracea
(Chatterjee and Chatterjee
2000
),
Azolla pinnata
(Masood and Abraham
2006
),
Brassica juncea
(John et al.
2009
). In contrary, Parys et al. (
1998
) in
Pisum
sativum
and (Bhattacharya et al. (
2010
) in
Paspalum distichum
reported no impact
of heavy metals on protein contents. However, Bhardwaj et al. (
2009
) in
Phaseolus
vulgaris
and Muneer et al. (
2011
) in
Vigna radiata
reported a substantial decrease.
Free Amino Acids
An increased level of free amino acids is an important criterion to assess stress tol-
erance/resistance in plants, specifically under drought (Mapelli et al.
2001
; Santos
and Pimentel
2009
), salinity (Dubey and Rani
1989
; Hartzendorf and Rolletschek
2001
), and heavy metal toxicity (Shah and Dubey
1998
). Metal-induced accumula-
tion of free amino acids, for example alanine, asparagine and proline, is the indi-
cation of disruption of metabolic activities in plants, which is crucially important
to cope with stressful conditions (El-Shintinawy and El-Ansary
2000
). Moreover,
accumulation of cysteine under heavy metal stress has been reported by El-Shintin-
awy and El-Ansary (
2000
) in
Glycine max
seedlings, which constitute a major por-
tion of total free amino acids. Similarly, Maheshwari and Dubey (
2008
) reported the
increased level of free amino acids under heat stress, which is essentially required
for the maintenance of developmental processes under stressful environments (Alia
and Saradhi
1991
; Chen et al.
2001
; Sengar et al.
2008
). An increased accumula-
tion of free amino acids as a result of heavy metal stress has also been reported in
Corchorus olitorius
(Mazen
2004
) and
Phaseolus vulgaris
(Bhardwaj et al.
2009
).
Proline
A plethora of literature is available on the accumulation of proline as an osmopro-
tectant under abiotic stresses, like salinity, low temperature, nutrient deficiencies,
drought and heavy metal toxicity (Stefl et al.
1978
; Goring
1979
; Carceller and
Fraschina
1980
; Aspinall and Paleg
1981
; Naidu et al.
1991
; Dubey and Pessarakli
