Agriculture Reference
In-Depth Information
Several complex and interlinked processes are involved
in cereal seed development. The starchy endosperm and
aleurone layer are formed and storage proteins, lipids and
polysaccharides are deposited in the endosperm. The mature
seeds contain only about 10-15% water. The starchy endosperm
cells do not survive this desiccation and undergo programmed
cell death, whereas the aleurone and embryo stay alive but
maintain a basal level of metabolic activity. Some proteins
were present throughout development (e.g., Cytosolicmalate
dehydrogenase) whereas others were associated with the early
grain fi lling (ascorbate peroxidase) or desiccation stages. Most
noticeably, the development process if characterized by an
accumulation of low molecular weight compounds, Į-amylase/
trypsin inhibitors, serine protease inhibitors and enzymes
involved in protection against oxidative stress (Finnie et al.
2002).
Low temperature may inhibit the photosynthetic rate
through the inactivation of enzymes in chloroplasts as well
as stomatal closure coupled by reduced water uptake. The
photosynthesis and transpiration of the rice plant, as shown
in Table 16 were considerably reduced by chilling at 5°C for 19
hrs, although no signs of chilling injury such as discolouration
and wilting were observed.
Table 16 Infl uence of low temperature on photosynthesis and transpiration of
rice plant (Tanaka and Yoshitomi 1973).
Before chilling
After chilling
3 hrs
4.5 hrs
12 hrs
Variety
02%
P
T
P
T
P
T
P
T
Nankai 43
21
13.4
3.2
3.6
1.7
1.0
1.4
11.3
2.2
03
17.9
3.0
0.9
1.5
17.8
2.4
IR 8
21
14.5
3.3
1.2
1.6
0.7
1.4
3.7
2.1
03
18.3
3.0
0.2
1.4
7.3
2.2
P = Photosynthesis (mgco 2 dm -2 , hr -1 )
T = Transpiration (g.dm -2 hr -1 )
Search WWH ::




Custom Search