Agriculture Reference
In-Depth Information
The critical air temperature for rooting is reported as
14-15.5ºC for seedlings in wetland seedbeds, 14-14.5ºC for
seedlings from semi-irrigated seed bed and 13-13.5ºC for
seedling from a dry land seed bed (Yatsuyanagi 1960).
When the seedlings of two rice cultivars, IR8 (low-
temperature sensitive) and Somewake (low-temperature
tolerant) were exposed to a low temperature of 15°C, the normal
increase in the chlorophyll content of the developing 4th leaf
blade ceased completely while increases in protein content
continued at a low rate in both cultivars. Analysis of soluble
and insoluble proteins in the 4th leaf blade of IR8 by SDS-
polyacrylamide gel electrophoresis revealed that synthesis of
RuBP carboxylase and several thylakoid proteins responsible for
photosynthetic electron transport and photophosphorylation
was greatly inhibited at low temperature. It was also found that
increases in the activities of some enzymes of the Calvin Cycle,
such as RuBPcarboxylase, fructose bisphosphatase and NADP-
glyceraldelye -3-P dehydrogenase as well as of catalase were
specifi cally inhibited during growth at the low temperature.
This results suggest that the synthesis of intracellular
components, in particular of key proteins required for
photosynthesis, is specially susceptible to low temperature
stress during development of rice leaves (Maruyama et al.
1990).
When seedlings of the rice cultivar K-Sen 4 were exposed,
at the germination and the leaf stages, to 5°C for 7 days, they
withered after incubation at 25°C. In contrast, the cultivar
Dunghan Sali showed chilling tolerance and successful growth
after rewarming (Saruyama and Tanida 1995). They also tried
to correlate the difference in cold sensitivity with superoxide
dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX),
and glutathione reductase (GR) (activated oxygen-scavenging
