The seed coat is specialized dead tissue protecting the plant embryo from mechanical and oxidative damage. Tannins, a type of flavonoids, are antioxidants known to accumulate in the Arabidopsis seed coat and transparent testa mutant seeds, deficient in flavonoid synthesis, exhibit low viability. However, their precise contribution to seed coat architecture and biophysics remains evasive. A seed coat cuticle, covering the endosperm outer surface and arising from the seed coat inner integument 1 cell layer was, intriguingly, previously shown to be more permeable in transparent testa mutants deficient not in cuticular component synthesis, but rather in flavonoid synthesis. Investigating the role of flavonoids in cuticle permeability led us to identify periclinal inner integument 1 tannic cell walls being attached, together with the cuticle, to the endosperm surface upon seed coat rupture. Hence, inner integument 1 tannic cell walls and the cuticle form two fused layers present at the surface of the exposed endosperm upon seed coat rupture, regulating its permeability. Their potential physiological role during seed germination is discussed.

中文翻译：

---

拟南芥种皮破裂时胚乳外表面单宁细胞壁的鉴定

种皮是专门的死组织，可保护植物胚免受机械和氧化损伤。单宁（一种类黄酮）是已知的抗氧化剂，其积累在拟南芥种皮和透明的睾丸突变种子中，缺乏类黄酮的合成，它们的生存能力较低。但是，它们对种皮结构和生物物理学的精确贡献仍在回避。有趣的是，先前显示，覆盖胚乳外表面并由种皮内被膜1细胞层产生的种皮表皮在透明睾丸中更具渗透性突变体不缺乏表皮成分合成，而是缺乏类黄酮合成。研究类黄酮在角质层通透性中的作用使我们确定了在种皮破裂后，沿角质层1的单宁细胞壁与角质层一起附着在胚乳表面。因此，在种皮破裂时，内被膜1单宁细胞壁和表皮形成两个融合层，存在于暴露的胚乳表面，调节其通透性。讨论了它们在种子萌发过程中的潜在生理作用。