Abstract
Temperature is the primary factor that affects seed dormancy and germination. However, the molecular mechanism that underlies its effect on dormancy alleviation remained largely unknown. In this study, we investigate hormone involvement in temperature induced germination as compared to that caused by after-ripening. Dormant (D) sunflower seeds cannot germinate at 10 °C but fully germinate at 20 °C. After-ripened seeds become non-dormant (ND), i.e. able to germinate at 10 °C. Pharmacological experiments showed the importance of abscisic acid (ABA), gibberellins (GAs) and ethylene in temperature- and after-ripening-induced germination of sunflower seeds. Hormone quantification showed that after-ripening is mediated by a decline in both ABA content and sensitivity while ABA content is increased in D seeds treated at 10 or 20 °C, suggesting that ABA decrease is not a prerequisite for temperature induced dormancy alleviation. GAs and ethylene contents were in accordance with germination potential of the three conditions (GA1 was higher in D 20 °C and ND 10 °C than in D 10 °C). Transcripts analysis showed that the major change concerns ABA and GAs metabolism genes, while ABA signalling gene expression was significantly unchanged. Moreover, another level of hormonal regulation at the subcellular localization has been revealed by immunocytolocalization study. Indeed, ABA, protein Abscisic acid-Insensitive 5 (ABI5), involved in ABA-regulated gene expression and DELLA protein RGL2, a repressor of the gibberellins signalling pathway, localized mainly in the nucleus in non-germinating seeds while they localized in the cytosol in germinating seeds. Furthermore, ACC-oxidase (ACO) protein, the key ethylene biosynthesis enzyme, was detected in the meristem only in germinating seeds. Our results reveal the importance of hormone actors trafficking in the cell and their regulation in specialized tissue such as the meristem in dormancy alleviation and germination.
Highlights
Seed dormancy and germination are complex adaptive traits of higher plants, they are determined by a combination of the degree of dormancy and environmental factors such as temperature, light, and oxygen[1,2]
To study the determinism of these processes, we analysed in sunflower seeds the abscisic acid (ABA), GAs and ethylene contents, the expression of genes involved in their synthesis or signalisation and the localization of some of their effectors in dormant conditions (D 10 °C) and dormancy breaking conditions by temperature (D 20 °C) or after ripening (ND)
A decrease in ABA content was observed in D 10 °C and ND 10 °C sunflower seeds after 15 h of imbibition
Summary
Seed dormancy and germination are complex adaptive traits of higher plants, they are determined by a combination of the degree of dormancy and environmental factors such as temperature, light, and oxygen[1,2]. Few months of after-ripening by dry storage breaks their dormancy, sunflower seeds become able to germinate at temperatures ranging from 5 to 40 °C, and their germination rate is enhanced at all temperatures[5]. Genetic and physiological studies have shown the important roles of the plant hormones, abscisic acid (ABA) and gibberellins (GAs) in seed dormancy. Other hormones such as ethylene and brassinosteroids, which both influence the ABA/GAs balance by counteracting ABA effects, promote germination[7]. ABA is a positive regulator of dormancy while GAs and ethylene release dormancy and promote the completion of germination by counteracting the effects of ABA2. ABA induces ABI5 expression to repress germination, and GAs promotes seed germination by enhancing the proteasome-mediated destruction of RGL2. Several ethylene mutants affected in ethylene metabolism or signaling, present differential sensitivity to ABA32
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
