Environmental Engineering Reference
In-Depth Information
the internal CO
2
concentration, integrity of membranes and proteins, metabolic
dysfunction, damage at the cellular and subcellular membrane levels via lipid
peroxidation, loss of activity of membrane-based enzymes, chloroplast capac-
ity, and PSII activities (Jones and Turner
1978
; Matsuda and Riazi
1981
; Kaiser
1987
; Asada
1992
; Hopkins and Hüner
1995
; Aziz and Larher
1998
; Nam et al.
1998
; Cornic
2000
; Wilson et al.
2000
; Lawlor
2002
; Velikova and Tsonev
2003
;
Flexas et al.
2004
; Hassan
2006
; Fariduddin et al.
2009
; Munns et al.
1979
). The
final result is a decline in net photosynthesis. The drought stress can reduce sto-
matal conductance and lead to decreased carbon assimilation, with consequently
low biomass production (Fariduddin et al.
2009
; Medrano et al.
2002
). Decrease
in photosynthetic efficiency is generally attributed to reduced CO
2
supply result-
ing from stomatal closure (Hsiao
1973
). A decrease in nitrate reductase activity
can inhibit protein synthesis, inactivate enzymes, and reduce the flux of nitrate to
the leaf (Fariduddin et al.
2009
; Morilla et al.
1973
; Shaner and Boyer
1976
). The
rapid loss of nitrate reductase activity could be part of a biochemical adaptation to
water deficit, shutting off the nitrate assimilation pathway and preventing accumu-
lation of nitrite and ammonium (Huffaker et al.
1970
).
Cell membranes, which are structurally composed of large amounts of polyunsatu-
rated fatty acid, are highly susceptible to react photolytically with possible changes in
membrane fluidity, permeability, and cellular metabolic functions (Bandyopadhyay et
al.
1999
). The elevation in the antioxidant system defences can detoxify the reactive
oxygen species generated by drought stress and can thereby recover the altered physi-
ological performance of stressed plants (Fariduddin et al.
2009
).
Water (drought) stress and high temperature together can cause a marked
decrease of PSII activity that, together with other functions, can lead to a signifi-
cant decrease in the net photosynthetic rate of plants (Hassan
2006
; Flagella et al.
1998
; Hassan et al.
1998
; Yordanov et al.
1997
,
1999
,
2000
). It has been shown
that this effect may be caused by stomatal and non-stomatal limitations. Stomatal
closure usually occurs before inhibition of photosynthesis and restricts CO
2
avail-
ability at the assimilation sites in chloroplast. In contrast, non-stomatal limitation
of photosynthesis has been attributed to reduced carboxylation efficiency, reduced
ribulose-1,5-bisphosphate (RuBP) regeneration, or inhibited chloroplast activity
(Wise et al.
1992
; Lawlor
1995
; Shangguan et al.
1999
). Conversely, water stress
mostly causes a progressive suppression of photosynthetic carbon assimilation in
desiccation-tolerant and intolerant wheat plants (Deltoro et al.
1998
).
The mechanism behind the water (drought) stress effect of decreasing photo-
synthesis is similar to that of high-irradiance/high temperature stress. It occurs
particularly in tropical and subtropical regions as mentioned before. Moreover,
water stress or drought in low temperature regions can decrease the water content
of plant cells that contain dissolved O
2
. Shortage of dissolved O
2
in response to
water stress can decrease the photoinduced generation of H
2
O
2
, which is directly
linked to photosynthesis. This effect can decrease photosynthesis and cause
decline in growth or death of organisms.
The water stress can shift the temperature threshold towards higher values
and cause an increase of the heat resistance (Yordanov et al.
1997
,
2000
; Havaux
