Structural Analysis of the Osmophores in Orchidantha chinensis var. longisepala

Osmophores specialized and defined on the labellum of Lowiaceae plants can produce a strong scent, unpleasant to humans but attractive to pollinators, which mimics the odor of carrion or decaying fruit during anthesis. In the present study, the labellum of Orchidantha chinensis var. longisepala was stained in vivo with neutral red to ascertain the location of osmophores. We used scanning electron microscopy (SEM) to observe the morphology of epidermal cells and transmission electron microscopy (TEM) to explore the ultrastructure of secretory cells. Results showed that osmophores of O. chinensis var. longisepala were located at adaxial surface of the upper labellum. Diverse epidermal cells and 1-2 layers of secretory cells comprised the osmophores. Cells of the glandular tissue showed enlarged nuclei compared to cells of nearby tissue and a dense cytoplasm. These cells also have more endoplasmic reticulum, mitochondria and plastids, sometimes dictyosomes. The scent substances were mainly from rupturing outer layer of the cuticle, and the diffusion of small molecules may contribute to the release. Research on the osmophores of Lowiaceae is useful to reveal the interactions between plants and pollinators and study the process of pollination.