College of Life Sciences, Shaanxi Normal University, Xi'an, 710119, Shaanxi, China.
Key Laboratory of Medicinal Plant Resource and Natural Pharmaceutical Chemistry of Ministry of Education, Shaanxi Normal University, Xi'an, 710119, Shaanxi, China.
Planta. 2024 Jun 7;260(1):21. doi: 10.1007/s00425-024-04453-8.
Petal developmental characteristics in Fumarioideae were similar at early stages, and the specialized nectar holder/pollen container formed by the outer/inner petals. The micro-morphology of these two structures, however, shows diversity in seven species. Elaborate petals have been modified to form different types, including petal lobes, ridges, protuberances, and spurs, each with specialized functions. Nectar holder and pollen container presumably have a function in plant-pollinator interactions. In Fumarioideae, four elaborate petals of the disymmetric/zygomorphic flower present architecture forming the "nectar holder" and "pollen container" structure at the bottom and top separately. In the present study, the petals of seven species in Fumarioideae were investigated by scanning electron microscopy, light microscope, and transmission electron microscopes. The results show that petal development could divided into six stages: initiation, enlargement, adaxial/abaxial differentiation, elaborate specializations (sacs, spurs, and lobes formed), extension, and maturation, while the specialized "nectar holder" and "pollen container" structures mainly formed in stage 4. "Nectar holder" is developed from the shallow sac/spur differentiated at the base of the outer petal, eventually forming a multi-organized complex structure, together with staminal nectaries (1-2) with individual sizes. A semi-closed ellipsoidal "pollen container" is developed from the apical part of the 3-lobed inner petals fused by middle lobes and attain different sizes. The adaxial epidermis cells are specialized, with more distinct punctate/dense columnar protrusions or wavy cuticles presented on obviously thickening cell walls. In addition, a large and well-developed cavity appears between the inner and outer epidermis of the petals. As an exception, Hypecoum erectum middle lobes present stamen mimicry. Elaborate petal structure is crucial for comprehending the petal diversity in Fumarioideae and provides more evidence for further exploration of the reproductive study in Papaveraceae.
花瓣在发育特征上具有相似性，其外花瓣和内花瓣共同形成特殊的花蜜托/花粉容器。然而，这两种结构的微观形态在 7 个物种中表现出多样性。精致的花瓣已经发生了改变，形成了不同的类型，包括花瓣裂片、脊、突起和距，每种都具有特殊的功能。花蜜托和花粉容器可能在植物与传粉者的相互作用中具有功能。在罂粟科，不对称/左右对称花的 4 个外花瓣呈现出结构，分别在底部和顶部形成“花蜜托”和“花粉容器”结构。在本研究中，使用扫描电子显微镜、光学显微镜和透射电子显微镜对罂粟科 7 个物种的花瓣进行了研究。结果表明，花瓣的发育可分为 6 个阶段：起始、扩大、背腹分化、精致特化（囊、距和裂片形成）、延伸和成熟，而特殊的“花蜜托”和“花粉容器”结构主要在第 4 阶段形成。“花蜜托”是由外花瓣基部分化的浅囊/距发育而来，最终形成一个多组织的复杂结构，与个体大小不一的雄蕊蜜腺（1-2）共同形成。一个半封闭的椭圆形“花粉容器”是由融合的中裂片的内花瓣的顶端发育而来，大小不同。腹表皮细胞特化，细胞壁明显增厚，具有更明显的点状/密集柱状突起或波浪状角质层。此外，花瓣的内、外表皮之间出现一个大而发育良好的腔。作为一个例外，Hypecoum erectum 中的中裂片呈现出雄蕊拟态。精致的花瓣结构对于理解罂粟科花瓣的多样性至关重要，并为进一步探索罂粟科生殖研究提供了更多证据。
