Abstract

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.

Highlights

  • Dormancy is a key ecological adaptation which protects seeds against germination during unfavourable conditions, such as during the winter period (Black et al 2008)

  • An analysis of Norway maple seed germination (Figs. 1, 2, 3), after dormancy breaking caused by cold stratification, showed that seeds started to germinate during week 7 of stratification, and by week 12, seeds reached 43% of germination

  • We present the results of an investigation of the association of abscisic acid (ABA) and GA signalling regulators with deep dormancy breaking caused by cold stratification

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Summary

Introduction

Dormancy is a key ecological adaptation which protects seeds against germination during unfavourable conditions, such as during the winter period (Black et al 2008). Seeds of some plant species are characterised by deep physiological dormancy, located in embryo tissues (Baskin and Baskin 2004). The mechanism of dormancy acquisition and breaking is complex and still far from completely understood, especially regarding deep physiological embryo dormancy. According to Luckwill’s (1952) theory, transition from dormancy to germination is under the antagonistic influence of inhibitors, such as abscisic acid (ABA), and promotors, such as gibberellins (GA). Investigating the regulation of the signal cascade involving ABA and GA at different levels could bring us closer to environmental and hormonal control of dormancy

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