Agriculture Reference
In-Depth Information
It is common to find a build up of non structural
carbohydrates in many parts of a plant under low temperature
conditions, a response indicating that growth is more sensitive
to low temperature than photosynthesis.
In response to extremes of temperature, plants can produce
various proteins that protect them from damaging effects
and falling rates of enzymes catalysis at low temperature so
also the photorespiration. As temperature fall, production
of anti freeze proteins rise. Cell membranes are also affected
by changes in temperature and can cause membrane to lose
its fl uid properties and become a gel in cold conditions. This
can affect the movement of molecules across the membrane.
In cold conditions more unsaturated fatty acids are placed in
the membrane. Various phenotypic symptoms in response to
chilling stress include reduced leaf expansion, wilting, chlorosis
and may lead to necrosis. Low temperature affects membrane
and depends on the proportion of unsaturated fatty acids in
it to the tolerance capacity so the conversion from fl uidity to
semi fl uidity is less which leads to solute leakage (Mahajan
and Tuteja 2005).
Infl uence of low temperature (chilling 5ºC for 19hr) on
photosynthesis (mgco
2
dm
-2
hr
-1
) and transpiration (g
.
dm
-2
h
-1
)
of rice plant (Tanaka and Yoshitomi 1973) is given hereunder.
Table 11
Infl uence of chilling and oxygen level on photosynthesis (mgco
2
dm
-2
h
-1
)
and transpiration (gdm
-2
h
-1
).
Before Chilling
After chilling
3 hr
4.5 hr
21 hr
Variety
O
2
%P
T
P
T
P
T
P
T
Nankai 23
21
13.4
3.2
3.6
1.7
1.0
1.4
11.3
2.2
3
17.9
3.0
0.9
1.5
-
-
17.8
2.4
IR8
21
14.5
3.3
1.2
1.6
0.7
1.4
3.7
2.1
3
18.3
3.0
0.2
1.4
-
-
7.3
2.2
