Environmental Engineering Reference
In-Depth Information
Sharkey
1987
; Huner et al.
1993
; Ebrahim et al.
1998
; Sundar and Ramachandra
Reddy
2001
; Caramori et al.
2002
; Kudoh and Sonoike
2002
; Yu et al.
2002
;
Huang and Guo
2005
). The latter effect can limit the photosynthetic rates or pro-
cesses of chilling-sensitive plants.
It is also shown that low temperatures can inhibit the enzymes of carbon assim-
ilation, such as fructose-1,6-bisphosphatase and sedoheptulose-1,7-bisphosphatase
(D'Ambrosio et al.
2006
; Sassenrath et al.
1990
; Sassenrath and Ort
1990
). It has
also been shown that the O
2
-induced inhibition of photosynthesis can increase
with temperature, from 12.2 % at 5 °C to 33.5 % at 35 °C (D'Ambrosio et al.
2006
). Plants of
B. vulgaris
exposed to low temperatures (5-15 °C) also show a
significant stimulation of CO
2
assimilation at 2 % O
2
concentration (D'Ambrosio
et al.
2006
). The inhibition of photosynthesis (photorespiration) at high tempera-
tures is generally caused by the increase of the ratio oxygenase/carboxylase activ-
ity of Rubisco (Sage and Sharkey
1987
).
It has been observed that low night temperature under chilling conditions
(mostly affected at 5 °C) can increase photoinhibition of photosynthesis with
a marked loss of D1 and 33 kDa proteins in various plants (Yang et al.
2009
;
Sundar and Ramachandra Reddy
2001
; Lidon et al.
2001
; Bertamini et al.
2006
).
This can be due to accumulation of soluble sugars and reduced orthophosphate
cycling from the cytosol back to the chloroplast. Therefore, it limits the ATP syn-
thesis needed for Rubisco regeneration (Ebrahim et al.
1998
; Hurry et al.
1998
).
Inhibition of photosynthetic electron transport is susceptible to lessen net pho-
tosynthesis in some chilling-sensitive plant species, despite relatively minimal
reductions in the ratio of variable to maximum chlorophyll (Chl) fluorescence
(
F
v
/
F
m
). Such an effect is due to the net photoinactivation of PSI rather than PSII
(Bertamini et al.
2006
; Tjus et al.
1998
; Sonoike
1999
). A significant decrease of
electron transport rate under chilling conditions might cause a low temperature-
induced limitation of carbon metabolism. Furthermore, sinks of electrons can
result in alternative processes to CO
2
fixation (D'Ambrosio et al.
2006
; Huner et
al.
1993
; Osmond
1981
; Hendrickson et al.
2003
,
2004
). The decrease of elec-
tron transport in PSII (D'Ambrosio et al.
2006
) is susceptible to decrease in the
photoinduced generation of O
2
•
−
and then H
2
O
2
, which is directly liked to the
occurrences of photosynthesis. The decrease in the contents of H
2
O
2
production
at chilling conditions can decrease the photosynthesis that subsequently decreases
the growth and development of plants. This effect is mostly responsible for other
physiological changes in plants at chilling stress.
It has also been observed that a significant increase of the proportion of elec-
tron flow in chilling conditions can occur in non-assimilative processes in some
plants, such as maize and grapevine leaves (Fryer et al.
1998
; Flexas et al.
1999
).
These studies suggest that a higher electron flow could reach O
2
, by the Mehler
reaction, as an alternative acceptor to CO
2
at low temperatures. This effect can
enhance the production of ROS such as O
2
•
−
and H
2
O
2
, which may not be used in
photosynthesis because of CO
2
shortage and other still unknown reasons. In con-
trast, H
2
O
2
and photogenerated HO
•
can damage the cells. Coherently, damage of
chlorophyll-protein complexes and pigments in has been observed in plant cells
