Rice is largely grown as a transplanted crop. Delay of
sowing and transplanting date may affect grain quality
due to the differences in temperature and solar radiation.
Late planting of the rice delays flowering time and results
in partial filling of the spikelets, thus lowering the milling
yield and head rice recovery during processing (Shahi
et al. 1975; Dhaliwal et al. 1986). The grain dimensions
(length/width) were also affected by late sowing and
transplanting, but resulted in higher protein content.
However, under these conditions, the amylose content
decreased (Dhaliwal et al. 1986). Reduction of amylose
may be to some extent due to the higher temperature
during grain filling because of the late sowing and transplanting.
It was reported that Wx gene expression was
increased in response to low temperature (18°C). The
longer rice plants were exposed to low temperature, the
higher the levels of Wx protein, and the greater the accumulation
of amylose (Hirano and Sano 1998). The G-T
polymorphism within the first intron of Wx gene has
been reported to be related to the different efficiency of
RNA splicing and processing when treated with low and
high temperatures during grain development (Larkin and
Park 1999). This could be one of the crucial reasons
behind the different level of Wx transcripts under different
temperature regimes. Besides Wx transcripts, SBEs
especially BEIIb were reported down-regulated due to
high temperature, whereas a-amylases were up-regulated
(Yamakawa et al. 2007). Apart from the effects on transcription,
the regulation of temperature is also reflected
by its influences on the activities of key enzymes for the
biosynthesis of starch (Cheng et al. 2003a; Jiang et al.
2003; Satoh et al. 2008). Thus, the structure and composition
of amylose and amylopectin are affected by temperature.
For instance, temperature change during grain
filling affects the chain length distribution of amylopectin
(Umemoto et al. 1999; Yamakawa et al. 2007). High temperature
also causes reduction in the amount of large
mature amyloplasts and increase in the number of small
immature amyloplasts containing small single starch granules
(Zakaria et al. 2002). Besides starch, storage protein
content is also affected by temperature. Elevated temperature
decreases accumulation of prolamin, which is consistent
with diminished expression of prolamin genes
(Yamakawa et al. 2007; Ma et al. 2009). On the other
hand, the relative content of glutelin is not changed in
response to high-temperature stress, but the relative content
of two glutelin subunits was reduced and the amount
of glutelin precursor was improved (Ma et al. 2009).
High-temperature stress results in a severe chalky appearance
which is due to changes in starch and protein
composition. Recently, a study on gene expression in
combination with metabolite measurements in rice endosperm
revealed several possible key steps for the inhibition
of starch accumulation and the accumulation of
amino acids in the developing caryopsis exposed to high
temperature. For instance, the import of sucrose into
endosperm cells might be impaired, but the supply of
certain amino acids was enhanced due to the high temperature,
which may eventually affect the starch and protein
biosynthesis. It provided us more comprehensive
knowledge of the mechanism behind high temperature
Rice is largely grown as a transplanted crop. Delay of
sowing and transplanting date may affect grain quality
due to the differences in temperature and solar radiation.
Late planting of the rice delays flowering time and results
in partial filling of the spikelets, thus lowering the milling
yield and head rice recovery during processing (Shahi
et al. 1975; Dhaliwal et al. 1986). The grain dimensions
(length/width) were also affected by late sowing and
transplanting, but resulted in higher protein content.
However, under these conditions, the amylose content
decreased (Dhaliwal et al. 1986). Reduction of amylose
may be to some extent due to the higher temperature
during grain filling because of the late sowing and transplanting.
It was reported that Wx gene expression was
increased in response to low temperature (18°C). The
longer rice plants were exposed to low temperature, the
higher the levels of Wx protein, and the greater the accumulation
of amylose (Hirano and Sano 1998). The G-T
polymorphism within the first intron of Wx gene has
been reported to be related to the different efficiency of
RNA splicing and processing when treated with low and
high temperatures during grain development (Larkin and
Park 1999). This could be one of the crucial reasons
behind the different level of Wx transcripts under different
temperature regimes. Besides Wx transcripts, SBEs
especially BEIIb were reported down-regulated due to
high temperature, whereas a-amylases were up-regulated
(Yamakawa et al. 2007). Apart from the effects on transcription,
the regulation of temperature is also reflected
by its influences on the activities of key enzymes for the
biosynthesis of starch (Cheng et al. 2003a; Jiang et al.
2003; Satoh et al. 2008). Thus, the structure and composition
of amylose and amylopectin are affected by temperature.
For instance, temperature change during grain
filling affects the chain length distribution of amylopectin
(Umemoto et al. 1999; Yamakawa et al. 2007). High temperature
also causes reduction in the amount of large
mature amyloplasts and increase in the number of small
immature amyloplasts containing small single starch granules
(Zakaria et al. 2002). Besides starch, storage protein
content is also affected by temperature. Elevated temperature
decreases accumulation of prolamin, which is consistent
with diminished expression of prolamin genes
(Yamakawa et al. 2007; Ma et al. 2009). On the other
hand, the relative content of glutelin is not changed in
response to high-temperature stress, but the relative content
of two glutelin subunits was reduced and the amount
of glutelin precursor was improved (Ma et al. 2009).
High-temperature stress results in a severe chalky appearance
which is due to changes in starch and protein
composition. Recently, a study on gene expression in
combination with metabolite measurements in rice endosperm
revealed several possible key steps for the inhibition
of starch accumulation and the accumulation of
amino acids in the developing caryopsis exposed to high
temperature. For instance, the import of sucrose into
endosperm cells might be impaired, but the supply of
certain amino acids was enhanced due to the high temperature,
which may eventually affect the starch and protein
biosynthesis. It provided us more comprehensive
knowledge of the mechanism behind high temperature
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