The micromorphological characterization, histo-phytochemical analysis and bioactivity of Tabernaemontana ventricosa Hochst. ex A. DC. (Apocynaceae)

Doctoral Degree. University of KwaZulu-Natal, Durban.

Medicinal plants are universally important due to their healing properties and pharmacological effects. Tabernaemontana ventricosa Hochst. ex A. DC. is a curative plant belonging to the Apocynaceae. The bark, stem, leaves, flowers, and latex of T. ventricosa are frequently used in ethnomedicine to palliate fever, treat wounds, and reduce high blood pressure. Due to the inconsistencies in the interpretation of specialized secretory structures within the Apocynaceae, the current study aimed to distinguish, for the first time, the type and distribution of the laticifers in the embryos, seedlings, and adult plants of T. ventricosa. Various microscopy techniques such as light microscopy, stereomicroscopy, fluorescence microscopy, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) were used for anatomical and morphological analysis. The histochemical, phytochemical, and biological activities (antibacterial, antioxidant, and cytotoxicity) were assessed using screening standard protocols. Moreover, Gas Chromatography-Mass Spectrometry (GC-MS) was conducted to identify the chemical composition of leaf, stem, and latex extracted with various solvents. Silver nanoparticles (AgNPs) were synthesized using various leaf, stem, and latex extracts. The AgNPs were characterized using UV-visible spectral analysis, Elemental Dispersive X-ray (EDX) spectroscopy, Fourier-Transform Infrared (FTIR) spectroscopy, Nanoparticle Tracking Analysis (NTA), and various microscopy methods. Additionally, AgNPs were evaluated for their biological activity using antibacterial and cytotoxicity assays. The current study indicated the presence of articulated anastomosing laticifers. The laticifers were found to have originated from ground meristematic and procambium cells and were randomly distributed in all ground and vascular tissue, displaying complex branching conformations. The presence of chemical constituents within the laticifers and latex revealed alkaloids, phenolics, neutral lipids, terpenoids, mucilage, pectin, resin acids, carboxylated polysaccharides, lipophilic and hydrophilic substances, and proteins. The GC-MS analysis revealed α-linolenic acid, pentadecanoic acid, α-d-mannofuranoside, methyl, 13-docosenamide, (Z)-, 9,12-octadecadienoic acid (Z,Z)-, lup-20(29)-en-3-ol, acetate, (3ꞵ), 9,19-cyclolanost-24-en-3-ol, (3ꞵ) and ꞵ-amyrin as significant components of the leaf, stem, and latex extracts. It is suggested that these major compounds are responsible for the considerable antibacterial, antioxidant, and cytotoxic activities of T. ventricosa extracts. Biologically synthesized AgNPs displayed a spherical, ovate, and triangular shape ranging from 4-80 nm across all treatments. The FTIR analysis showed that alcohols, carboxylic acids, phenolics, and alkanes are possibly responsible for the capping of silver (Ag) ions, and the NTA data suggests that synthesized AgNPs fluctuated from stable to unable particles, which was treatment dependent. Due to the outcomes of biologically active compounds produced by this species, further studies are necessary to establish the potential medicinal properties of T. ventricosa.