Environmental Engineering Reference
In-Depth Information
Industries dealing with tannins, paper, vegetable oil/ghee, cosmetics and phar-
maceuticals continuously discharge heavy metal-containing effluents in irrigation
system (Nabi et al.
2001
). In Pakistan, heavy metal concentrations in soil and water
are currently within the maximum permissible limits (Ghafoor
2000
; Nabi et al.
2001
), and cause no visible toxicity in agricultural crops (Alloway
1995
). However,
continuous use of these metals-polluted will be the major hazard that will limit crop
growth and productivity in the near future.
3
Metal-Induced Regulation of Growth
and Physio-Anatomical Attributes
3.1
Growth Attributes
Heavy metals severely affect growth and development of plants, which is mainly
due to their effect on plant biomass production, photosynthetic pigment concen-
tration, gas exchange characteristics and uptake of micro- and macro-nutrients
(Burzynski and Klobus
2004
).
Root growth is generally more affected due to metal stress as compared to the
shoot growth (Souza et al.
2005
); however, reduction in biomass has earlier been
reported by several authors, e.g., Jadia and Fulekar (
2008
) in
Medicago sativa,
Aziz
et al. (
2007
) in
Hibiscus sabdariffam
Chatterjee and Chatterjee (
2000
) in
Brassica
oleracea
var.
botrytis
cv. Maghi, Ali et al. (
2003
) in
Salix acmophylla,
Hussain et al.
(
2006
) in
Azolla pinnata
and Mukhtar et al. (
2010
) in
Heianthus annuus
.
3.2
Physiological Attributes
3.2.1
Gas Exchange Characteristics
Heavy metals directly affect photosynthesis and other gas exchange attributes in
plants (Pang et al.
2003
; Jing et al.
2005
; Kaznina et al.
2005
; Mukhtar et al.
2010
).
A reduction in net photosynthetic rate (Bishnoi et al.
1993
; Krupa and Baszynski
1995
), stomatal conductance (Bethkey and Drew
1992
), transpiration rate (Chatterjee
and Chatterjee
2000
; Pandey and Sharma
2002
) and water use efficiency (Bishnoi
et al.
1993
) has earlier been reported in plants under heavy metal stress. However, an
increase in intercellular CO
2
concentration has been reported by Seregin and Ivanov
(
2001
).
Stomatal regulation may be one of the major factors affecting photosynthetic
rate, which may be mainly due to direct effect on stomatal regulation that may be
due to amendment in K fluxes inside the guard cells. This may result in stoma-
tal closure that reduces exchange of gasses and ultimately the photosynthetic rate
(Bishnoi et al.
1993
; Vernay et al.
2007
). Another factor affecting photosynthetic
