Holloway Thomas, Steinbrecher Tina, Pérez Marta, Seville Anne, Stock David, Nakabayashi Kazumi, Leubner-Metzger Gerhard
Department of Biological Sciences, Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK.
Syngenta, Jealott's Hill International Research Centre, Warfield, Bracknell,, RG42 6EY, UK.
New Phytol. 2021 Feb;229(4):2179-2191. doi: 10.1111/nph.16948. Epub 2020 Oct 16.
How the biophysical properties of overlaying tissues control growth, such as the embryonic root (radicle) during seed germination, is a fundamental question. In eudicot seeds the endosperm surrounding the radicle confers coat dormancy and controls germination responses through modulation of its cell wall mechanical properties. Far less is known for grass caryopses that differ in tissue morphology. Here we report that the coleorhiza, a sheath-like organ that surrounds the radicle in grass embryos, performs the same role in the grass weed Avena fatua (common wild oat). We combined innovative biomechanical techniques, tissue ablation, microscopy, tissue-specific gene and enzyme activity expression with the analysis of hormones and oligosaccharides. The combined experimental work demonstrates that in grass caryopses the coleorhiza indeed controls germination for which we provide direct biomechanical evidence. We show that the coleorhiza becomes reinforced during dormancy maintenance and weakened during germination. Xyloglucan endotransglycosylases/hydrolases may have a role in coleorhiza reinforcement through cell wall remodelling to confer coat dormancy. The control of germination by coleorhiza-enforced dormancy in grasses is an example of the convergent evolution of mechanical restraint by overlaying tissues.
覆盖组织的生物物理特性如何控制生长，比如种子萌发期间的胚根，是一个基本问题。在双子叶植物种子中，围绕胚根的胚乳赋予种皮休眠特性，并通过调节其细胞壁机械特性来控制萌发反应。对于组织形态不同的禾本科颖果，人们了解得要少得多。在此我们报告，在禾本科杂草野燕麦中，胚根鞘（一种包围禾本科植物胚根的鞘状器官）发挥着与双子叶植物种子中胚乳相同的作用。我们将创新的生物力学技术、组织切除、显微镜观察、组织特异性基因和酶活性表达与激素和寡糖分析相结合。综合实验工作表明，在禾本科颖果中，胚根鞘确实控制着萌发，对此我们提供了直接的生物力学证据。我们发现，胚根鞘在休眠维持期间得到强化，在萌发期间变弱。木葡聚糖内转糖基酶/水解酶可能通过细胞壁重塑在胚根鞘强化过程中发挥作用，从而赋予种皮休眠特性。禾本科植物中胚根鞘强制休眠对萌发的控制是覆盖组织机械限制趋同进化的一个例子。
