Paul Shobhon, Saha Pallabi, Mitra Adinpunya
Natural Product Biotechnology Group, Agricultural and Food Engineering Department, Indian Institute of Technology, Kharagpur, 721302, India.
Protoplasma. 2025 May 28. doi: 10.1007/s00709-025-02073-x.
Calyx nectaries are common secretory structures in Clerodendrum (Lamiaceae) that play an important role in plant indirect defence. These structures possess intricate morphological and anatomical features that are associated with the secretion physiology. This study intended to elucidate the structurally homologous calyx nectary glands of two Clerodendrum species that undergo morphological and anatomical changes facilitating nectar secretion. The morpho-anatomical, histochemical and ultrastructural features of the calyx nectary glands in two Clerodendrum species, viz., C. chinense and C. infortunatum, were studied throughout floral maturation stages using light and electron microscopy. The flower calyx possesses distinct disc-shaped patelliform nectary glands with different morphologies in both species. Histological analyses revealed distinct tissue regions in the nectary glands in both species. The nectary glands showed well-defined palisade-like secretory epidermis bounded by cuticular covering, lipid-rich intermediate layer, nectary parenchyma with prominent vascular bundles and photosynthetically active sub-nectary parenchyma tissue. Ultrastructural analysis revealed the presence of dense cytoplasm with a large number of mitochondria and chloroplasts in the nectariferous region in both species. Starch granules were found to be present within the chloroplasts and leucoplasts, and their depletion was noted in both the species, more prominently in C. infortunatum, suggesting their possible role in nectar biosynthesis. Anatomically, the calyx nectaries in both species were shown to be homologous and conserved which showed differential changes in both cell and tissue levels throughout floral maturation. Synthesis of nectar components in the nectary parenchyma supplemented with vascular supply and their regulation by hydrophobic barrier could shed light on the nectar biosynthesis and secretion process. Also understanding these nectary structures in taxonomic groups can provide valuable insights into phylogenetic relationships within the genus.
花萼蜜腺是唇形科大青属植物中常见的分泌结构，在植物间接防御中发挥着重要作用。这些结构具有复杂的形态和解剖特征，与分泌生理相关。本研究旨在阐明两种大青属植物中结构同源的花萼蜜腺，它们经历形态和解剖变化以促进花蜜分泌。利用光学显微镜和电子显微镜，在整个花期成熟阶段研究了两种大青属植物（即华大青和臭牡丹）花萼蜜腺的形态解剖、组织化学和超微结构特征。两种植物的花萼均具有明显的盘状碟形蜜腺，形态各异。组织学分析揭示了两种植物蜜腺中不同的组织区域。蜜腺具有界限分明的栅栏状分泌表皮，表皮有角质层覆盖，富含脂质的中间层，有突出维管束的蜜腺薄壁组织以及具有光合活性的蜜腺下薄壁组织。超微结构分析显示，两种植物的泌蜜区域均存在含有大量线粒体和叶绿体的致密细胞质。淀粉粒存在于叶绿体和白色体中，并且在两种植物中均观察到淀粉粒的消耗，在臭牡丹中更为明显，这表明它们可能在花蜜生物合成中发挥作用。从解剖学上看，两种植物的花萼蜜腺显示出同源且保守的特征，在整个花期成熟过程中，细胞和组织水平均出现了不同的变化。蜜腺薄壁组织中花蜜成分的合成以及维管供应的补充，以及疏水屏障对其的调节，可能有助于揭示花蜜的生物合成和分泌过程。此外，了解分类群中的这些蜜腺结构可以为该属内的系统发育关系提供有价值的见解。
