Ultrastructure and development of acanthocytes, specialized cells in <i>Stropharia rugosoannulata</i>, revealed by scanning electron microscopy (SEM) and cryo-SEM

Acanthocytes are special cells with a distinct spiky shape produced exclusively by the fungi of <i>Stropharia</i> and can be used to defend against nematodes. In the present study, the ultrastructure and development of acanthocytes were revealed by scanning electron microscopy (SEM) and cryo-SEM in <i>S. rugosoannulata</i>, a popular cultivated mushroom both in China and Europe. The acanthocytes were abundant on the surface of rhizomorph, casing soils, and vegetative mycelia of homokaryotic and heterokaryotic strains in <i>S. rugosoannulata</i>. The development of the acanthocyte was investigated with cryo-SEM, which has distinct advantage for observation of the ultrastructure of live, hydrated structures. Three distinct stages, including formation of lateral branch that was covered with patches, spiky structure formation, and maturation of acanthocytes, were identified and described. The irregular patches deposited on the surface of lateral branches and the holes in the spiky branches of the acanthocytes were reported for the first time. The environmental nitrogen level showed impact on acanthocyte production, but it seemed not to be the indispensable factor. Acid medium could delay the initiation of the acanthocyte formation but did not affect the overall morphology and structure, indicating that the central deposit of acanthocytes should be acid soluble. Acanthocytes of <i>S. rugosoannulata</i> have similar hydrophobicity to mycelia. The observation of ultrastructure and development process of acanthocytes provides insights into the ecological function and evolution of this special structure.棘细胞（Acanthocytes）是一类具有独特尖刺形态的特殊细胞，仅由球盖菇属（*Stropharia*）真菌产生，可用于抵御线虫。本研究通过扫描电子显微镜（SEM）与冷冻扫描电子显微镜（cryo-SEM），对大球盖菇（*Stropharia rugosoannulata*）——一种在中国与欧洲均广受欢迎的栽培食用菌——的棘细胞超微结构与发育过程进行了系统解析。棘细胞在大球盖菇的根状菌索、覆土基质以及同核与异核菌株的营养菌丝表面广泛分布。本研究借助冷冻扫描电子显微镜开展棘细胞发育的观测，该技术对活体含水结构的超微结构观测具有独特优势。研究鉴定并描述了三个明确的发育阶段：带斑块覆盖的侧枝形成、尖刺结构构建以及棘细胞成熟。本研究首次报道了沉积在侧枝表面的不规则斑块，以及棘细胞尖刺分支上存在的孔洞。环境氮水平对棘细胞的产生具有调控作用，但并非其形成的必需因子。酸性培养基可延缓棘细胞形成的起始进程，但不会改变其整体形态与结构，这表明棘细胞的中心沉积物质应为酸溶性物质。大球盖菇的棘细胞与菌丝具有相似的疏水性。对棘细胞超微结构与发育过程的观测，为这一特殊结构的生态功能与演化研究提供了重要的研究视角。