Sorbonne Université, CNRS, Biologie du développement Paris Seine - Institut de Biologie Paris Seine, LBD - IBPS, 75005, Paris, France.
Department of Cell and Systems Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada.
Sci Rep. 2019 Mar 19;9(1):4861. doi: 10.1038/s41598-019-40494-w.
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 (GA 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.
温度是影响种子休眠和萌发的主要因素。然而，其缓解休眠作用的分子机制在很大程度上仍然未知。在这项研究中，我们研究了激素在温度诱导萌发中的作用与后熟诱导萌发的区别。休眠（D）向日葵种子在 10°C 时不能萌发，但在 20°C 时完全萌发。后熟种子变成非休眠（ND），即能够在 10°C 时萌发。药理学实验表明，脱落酸（ABA）、赤霉素（GA）和乙烯在向日葵种子的温度和后熟诱导萌发中起着重要作用。激素定量表明，后熟是通过 ABA 含量和敏感性的下降来介导的，而在 10 或 20°C 处理的 D 种子中 ABA 含量增加，这表明 ABA 减少不是温度诱导休眠缓解的先决条件。GA 和乙烯含量与三种条件下的萌发潜力一致（D 20°C 和 ND 10°C 中的 GA 高于 D 10°C）。转录本分析表明，主要变化涉及 ABA 和 GA 代谢基因，而 ABA 信号基因的表达则没有明显变化。此外，通过免疫细胞化学定位研究揭示了激素在亚细胞定位水平上的另一种调控方式。事实上，ABA、ABA 不敏感蛋白 5（ABI5），参与 ABA 调节基因表达和赤霉素信号通路的 DELLA 蛋白 RGL2，在非萌发种子中主要定位于细胞核，而在萌发种子中定位于细胞质。此外，乙烯生物合成酶关键酶 ACC-氧化酶（ACO）蛋白仅在萌发种子的分生组织中被检测到。我们的研究结果揭示了激素在细胞内运输和在分生组织等专门组织中的调节在休眠缓解和萌发中的重要性。
