One of the first changes upon imbibition is the resumption
of respiratory activity, which can be detected within minutes.
After a steep initial increase in oxygen consumption,
the rate declines until the radicle penetrates the surrounding
structures. At this time, another burst of respiratory activity
occurs (Botha et al., 1992; Bewley and Black, 1994). The
glycolytic and oxidative pentose phosphate pathways both
resume during phase I, and the Kreb's cycle enzymes become
activated (Nicolas and Aldasoro, 1979; Salon et al.,
1988). Germinating seeds of many species frequently produce
ethanol (Morohashi and Shimokoriyama, 1972). This is
often the result of an internal deficiency in oxygen that is
caused by restrictions to gaseous diffusion by the structures
that surround the seed and by the dense internal structure of
most seeds. This oxygen deficiency may result in more
pyruvate production than utilization for activities of the
Kreb's cycle and electron transport chain.