The shading treatment which decreases light intensity affects the ornamental characteristics in herbaceous peony (Paeonia lactiflora Pall.), including flower color, leaf shape and stem straightness. However, the morphological, microstructural and lignin-related responses of its stems to shading have not been systematically and deeply studied. Here, we focused on these responses to shading treatment in herbaceous peony stems. Morphological results showed that shading treatment significantly bended stems, decreased stem diameters, lightened stem weights and reduced stem strength. Microstructural observations demonstrated that shading treatment decreased vascular bundle number, xylem area, xylem ratio and secondary cell wall (SCW) thickness. Lignin-related analysis revealed that shading treatment markedly decreased lignin content in cell walls especially S-lignin and G-lignin, deposition in SCWs and related enzyme activities. Furthermore, transcriptomic analysis showed that shading treatment suppressed lignin-related processes, lignin biosynthetic pathway and lignin-related transcriptional activators. Collectively, shading treatment suppressed lignin biosynthesis and reduced lignin deposition in SCW, leading to undeveloped secondary xylem and bender stems. These findings provide a fundamental understanding of the morphological, microstructural and lignin-related responses of herbaceous peony stem to shading.

降低光照强度的遮光处理影响了芍药（Paeonia lactiflora）的观赏特性Pall.)，包括花色、叶形和茎直度。然而，其茎对遮荫的形态、微观结构和木质素相关反应尚未得到系统和深入的研究。在这里，我们专注于对草本牡丹茎的遮荫处理的这些反应。形态学结果表明，遮荫处理显着弯曲茎，减小茎直径，减轻茎重量并降低茎强度。微观结构观察表明，遮光处理减少了维管束数量、木质部面积、木质部比例和次生细胞壁 (SCW) 厚度。木质素相关分析表明，遮荫处理显着降低了细胞壁中的木质素含量，尤其是 S-木质素和 G-木质素、SCW 中的沉积和相关酶活性。此外，转录组学分析表明，遮荫处理抑制了木质素相关过程、木质素生物合成途径和木质素相关转录激活剂。总的来说，遮荫处理抑制了木质素生物合成并减少了 SCW 中的木质素沉积，导致未发育的次生木质部和弯曲茎。这些发现为草本牡丹茎对遮荫的形态、微观结构和木质素相关反应提供了基本的理解。