lmbibition and the Resumption of Metabolism
Uptake of water by a mature dry seed is triphasic (Figure I),
with a rapid initial uptake (phase I) followed by a plateau
phase (phase 11). A further increase in water uptake occurs
only after germination is completed, as the embryonic axes
elongate. Because dormant seeds do not complete germi-
nation, they cannot enter phase 111.
The influx of water into the cells of dry seeds during phase
I results in temporary structural perturbations, particularly to
membranes, which lead to an immediate and rapid leakage
of solutes and low molecular weight metabolites into the
surrounding imbibition solution. This is symptomatic of a
transition of the membrane phospholipid components from
the gel phase achieved during maturation drying to the nor-
mal, hydrated liquid-crystalline state (Crowe and Crowe,
1992). Within a short time of rehydration, the membranes re-
turn to their more stable configuration, at which time solute
leakage is curtailed.