Metabolism of Dormancy Maintenance and Termination
Some seeds lose their dormancy while still in the dry state
(during afterripening), when their rate of metabolism is very
Iow. However, imbibed, dormant seeds are metabolically
very active and in this state can receive an externa1 signal
(e.g., light, chilling, alternating temperatures, and chemical
or hormonal treatment) that can stimulate germination. The
primary events in the release from dormancy are the recep-
tion of the stimulus by the embryo and the immediate signal
transduction chain that leads to the secondary events,
which could involve metabolic and hormonal changes (Fig-
ure 2). The final result is emergence of the embryonic axis
from the seed, that is, the completion of germination. Of the
primary events, the role of phytochrome is well known, al-
though what occurs after the active form, Pfr, is produced is