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Doctoral Degrees (Biological Sciences)

Permanent URI for this collectionhttps://hdl.handle.net/10413/12381

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Browsing Doctoral Degrees (Biological Sciences) by Author "Adu, Oluwatosin Temilade."

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    Micromorphology and biological activities of leaves and stem bark of Diospyros villosa (L.) De Winter.
    (2021) Adu, Oluwatosin Temilade.; Naidoo, Yougashree.; Lin, Johnson.
    Review Article: The genus Diospyros consists of many species which are distributed throughout the world. There is no elaborate information about the holistic importance of the plants. This review aims to delve for more information about the usefulness of the plants for humans. A detailed study of the genus Diospyros with a targeted focus on Diospyros villosa (L.) De Winter plant was carried out information on the plants’ morphology was taken as observed during harvest. Other information with respect to geographical distribution, secretory structures, chemical composition, embedded bioactive constituents and the associated mechanism of action of the bioactive constituents were acquired. The genus Diospyros yields products of medicinal importance throughout the world. This study gives some detailed information about the genus Diospyros as well as the potential use of the species as functional medicinal plants with bioactive compounds. Manuscript 1: This study evaluated the phytochemical constituents, antioxidant and antimicrobial potentials of Diospyros villosa (L.) De Winter leaves and stem bark. The extracts were obtained using different media (methanol, chloroform and hexane). DPPH and FRAP methods were used to investigate the antioxidant potentials of the crude extracts. The antimicrobial potency of Diospyros villosa extracts against five pathogenic bacteria was determined using MIC, MBC and agar well diffusion methods. Flavonoids, alkaloids and phenols were identified in D. villosa extracts. The mean concentrations of methanol extracts Diospyros villosa leaves and stem against DPPH providing 50% inhibition were 9.53 ± 0.25 μg ml-1 and 9.52 ± 0.30 μg ml-1 respectively. The methanolic leaves extracts further showed promising antimicrobial activity against Klebsiella pneumonia, Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus and Staphylococcus aureus with inhibition zones which are almost as high as the control. The antimicrobial methods also demonstrated that the leaves and stem bark extracts had wide antimicrobial abilities. The results revealed that D. xxvii villosa leaves and stem bark contain reasonable amount of bioactive compounds. Hence, these compounds may serve as natural antioxidants and antibacterial agents for the treatment of bacterial infections and diseases. Manuscript 2: Nanoparticles are synthesized through wet chemical techniques. Meanwhile, the chemicals used often are toxic and flammable. While considering safe substances, Diospyros villosa leaves and stem bark are both observed to be suitable for the biosynthesis of silver nanoparticles. In this research study, we described a less expensive and environmental-friendly technique for the biosynthesis of silver nanoparticles from silver nitrate (AgNO3) solution and Diospyros villosa extracts. The obtained silver nanoparticles were characterized using the UV-vis absorption spectroscopy, FT-IR, EDX, SEM and TEM, DPPH scavenging ability, ferric reducing antioxidant potential, antimicrobial susceptibility and quorum sensing inhibition tests. The biosynthesized silver nanoparticles showed good antibacterial activity against Escherichia coli, Staphylococcus aureus, Staphylococcus epidermis and Enterococcus faecalis. The D. villosa nanoparticles demonstrated potential antioxidant and quorum sensing inhibition and may thus represent a source of antioxidant as well as quorum sensing inhibition candidate for infection and disease control. Manuscript 3: The structural adaptation, histological compatibility and ecological functions of trichomes in Diospyros villosa, however remain largely unclear. This study aimed to interpret the structure and histochemical analysis of the leaves and stem bark of Diospyros villosa using light and electron microscopy and different histochemical tests as well as to elucidate the composition of the secretory products. Trichome density and length were also determined in three developmental stages of the leaves. The results of histochemical tests also revealed the presence of alkaloids and phenolic compounds which are medicinally important and used to treat multiple ailments. xxviii Manuscript 4: Diospyros villosa is traditionally used for processing anti-bacterial properties. Its cytotoxic effects have not been studied before. Therefore, this study aimed to examine the nutritional properties as well the cytotoxic effects of D. villosa. The leaves and stem barks were subjected to three different extraction methods (methanol, chloroform and hexane) and their nanoparticles were synthesized at two different temperatures (room temperature and at 80 ºC). Thereafter, extracts were assessed using the associated AOCC protocols, for their nutritional content (moisture, fibre, proteins, lipid, ash and hydrolysable carbohydrates). Diospyros villosa extracts and their corresponding nanoparticles were then incubated overnight with cancerous and noncancerous cell lines to evaluate their cytotoxic potential.