Agriculture Reference
In-Depth Information
of a lack of carbohydrate necessary for growth. Under these
conditions, low temperature may produce more tillers. When
light is adequate, however, higher temperatures increase tiller
number (Yoshida 1973) the effects of low air humidity and low
root temperature on water uptake and growth indicated that
the daily transpiration of the plants grown at low humidity
was 1.5 to 2 fold higher than that at high humidity. Low root
temperature (LRT) at 13ºC reduced transpiration, and the extent
was larger at lower humidity. LRT also reduced total dry matter
production and leaf area expansion and the extent was again
larger at lower humidity. These observations suggest that the
suppression of plant growth by LRT is associated with water
stress due to decreased water uptake ability of the root.
It is indicated, that there is a positive relationship between
root oxidizing activity and dry matter production in rice
seedlings. Root oxidizing activity in the cold tolerant variety
was higher than in the cold-susceptible one under chilling
conditions, suggesting it could be used as one of the criteria
for selecting cold-tolerant rice varieties. Where root oxidizing
activity fell to about 2 mg NA/2 hrs/g dryroot, dry matter
production of rice seedlings stops and probably, this value was
near the threshold for dry matter production (Table 7). The
activity of peroxidase was also related to the root oxidizing
activity under low temperature so that peroxidase can be
used as another parameter for selecting cold-tolerant varieties.
Content of proteins in rice roots is one of the mechanisms of
rice resistance or adoption to a low temperature stress. Severe
chilling stress decreased the amounts of DNA and RNA
indicating a suppression of transcription process (Dai 1988).
Top growth of the rice plants after transplanting is, in
general, linearly accelerated by raising average temperature
from an approximately 18°C to 33°C. Above and below this
range the growth decreases notably. Water temperature is
