Signalling regulators of abscisic and gibberellic acid pathways are involved in dormancy breaking of Norway maple (Acer platanoides L.) seeds

Physiological dormancy is a characteristic of the seeds of plants that are exposed to adverse harsh environmental conditions. Many tree seeds from the northern hemisphere have acquired deep dormancy as an adaptation to the winter period. Such kinds of dormancy can be removed by cold stratification. This physiological process is regulated through abscisic and gibberellic acids signal transduction, in which ABI5, 14-3-3 and RGL2 have a negative response to cold stratification and cause dormancy breaking. Our study is, to our knowledge, the first to report tissue localisation of ABI5 and RGL2 in deeply physiologically dormant seeds. Localisation of these proteins differs in time (weeks of stratification) and space (anatomy of the embryo root). Studies showed that changes occurred on three levels: (1) tissue, as the fluorescence signal throughout the weeks of stratification was localised in different regions of the embryo axes, and these changes were associated with changes in development regulation of the individual regions; (2) cell, either in nucleus or in cytoplasm, involving regulation of gene expression, and synthesis and inactivation in cytoplasm; and (3) organelle, specifically in nuclei/nucleoli, indicating transcription regulation of the specific genes. At the end of stratification, when dormancy is broken, ABI5 and RGL2 were not noticeable in the cells of the apical meristem. ABI5 likely blocked germination through inhibition of meristem activity, whereas RGL2 through blocking of procambial cell differentiation. We speculate that similar molecular and cellular mechanisms exist among other seeds characterised by physiological dormancy.