The beneficial effects of cold stratification on breaking
dormancy and promoting seed germination of many tree species
including Acer are well recognized. However, we lack a full understanding
of the biochemical and cell ultrastructural changes
during cold stratification. In our study, 12 weeks of cold stratification
were required for dormancy break, during which the ABA/GA3,
4, 7 ratio decreased and storage proteins and lipids were hydrolyzed,
resulting in changes in sugars and amino acids. Furthermore, cell
division and embryo axis growth occurred late in the cold sratifi-
cation period. Then, radicle emergence soon followed in seeds
incubated at a warm temperature and in those kept at 5 C for a
short period following dormancy break. Although we have shown
that biochemical and cell ultrastructural changes occur in seeds of
A. morrisonense during the dormancy breaking cold stratification
process, identification of the precise dormancy breaking mechanism
requires further study