Agriculture Reference
In-Depth Information
Under suitable conditions, the seed absorbs water about
25% of its dry weight.
Imbibition is the rehydration of seed through the physical
process of diffusion of water. According to Engels et al. (1986)
the diffusion of water in white rice at 30ºC is 5.2 X 10
-11
m²/s.
Cold temperature slows down the diffusion. The imbibition
phase of germination is considered to be the most sensitive one,
which leads to the escape of solutes from the seeds. In spite
of the imbibition being considered the most sensitive phase,
Yoshida (1981a) reported that the greatest infl uence of cold
temperature on germination occurs in the subsequent phases
of activation and growth of coleoptile and radical (Figs. 1 & 2).
Cold temperature effects due to unbalanced metabolic activities
retard the cell elongation and cell division (Lyons 1973).
Data indicates that the temperature range at which rice
seeds can germinate is between near 0ºC and 45ºC. The optimal
temperature however is narrower. According to Nishiyama
(1976) the optimal temperature for germination of rice seeds
is estimated to range from approximately 18ºC to 33ºC. 30ºC is
Fig. 1
Timings of metabolic activities in seed germination.
