Proteome analysis of Norway maple (Acer platanoides L.) seeds dormancy breaking and germination: influence of abscisic and gibberellic acids

Abstract

Background: Seed dormancy is controlled by the physiological or structural properties of a seed and the external conditions. It is induced as part of the genetic program of seed development and maturation. Seeds with deep physiological embryo dormancy can be stimulated to germinate by a variety of treatments including cold stratification. Hormonal imbalance between germination inhibitors (e.g. abscisic acid) and growth promoters (e.g. gibberellins) is the main cause of seed dormancy breaking. Differences in the status of hormones would affect expression of genes required for germination. Proteomics offers the opportunity to examine simultaneous changes and to classify temporal patterns of protein accumulation occurring during seed dormancy breaking and germination. Analysis of the functions of the identified proteins and the related metabolic pathways, in conjunction with the plant hormones implicated in seed dormancy breaking, would expand our knowledge about this process.

Results: A proteomic approach was used to analyse the mechanism of dormancy breaking in Norway maple seeds caused by cold stratification, and the participation of the abscisic (ABA) and gibberellic (GA) acids. Forty-four proteins showing significant changes were identified by mass spectrometry. Of these, eight spots were identified as water-responsive, 18 spots were ABA- and nine GA-responsive and nine spots were regulated by both hormones. The classification of proteins showed that most of the proteins associated with dormancy breaking in water were involved in protein destination. Most of the ABA- and GA-responsive proteins were involved in protein destination and energy metabolism.

Conclusion: In this study, ABA was found to mostly down-regulate proteins whereas GA up-regulated proteins abundance. Most of the changes were observed at the end of stratification in the germinated seeds. This is the most active period of dormancy breaking when seeds pass from the quiescent state to germination. Seed dormancy breaking involves proteins of various processes but the proteasome proteins, S-adenosylmethionine synthetase, glycine-rich RNA binding protein, ABI3-interacting protein 1, EF-2 and adenosylhomocysteinase are of particular importance. The effect of exogenously applied hormones was not a determining factor for total inhibition (ABA) or stimulation (GA) of Norway maple seed dormancy breaking and germination but proteomic data has proven these hormones play a role.

Figure 1

Germination (at 3°C) of Norway maple seeds after imbibition (in water or in solutions of ABA or GA) and stratification at 3°C. Error bars represent standard errors, n = 4.

Figure 2

Positions of the main varying spots on 2D PAGE silver-stained gels of Norway maple seeds during dormancy breaking and germination. Proteome variation during stratification: (A) in water only, (B) with ABA, (C) with GA. These are the positions of the 44 mapped and identified spots indicated in the master gels (combining the analytical results of 1200 spot groups) by the number that appears in Additional file 1. Specific spots are described as showing variations during stratification in water and between stratification with ABA or GA and stratification in water only.

Figure 3

Assignment of the 44 identified variable protein spots to functional categories using the classification of Bevan et al. [19]. (A) Proteins associated with dormancy breaking in water; (B) Proteins regulated by ABA; (C) Proteins regulated by GA.