Ida Risenga

In preparation for cryopreservation, Eucalyptus grandis in vitro axillary buds were dried over silica gel. Pretreatment of the buds with 5 mg per L ABA resulted in partial resistance to water loss (0.76 to 0.45 g per g fresh mass basis) as compared with untreated buds (0.76 to 0.33 g per g) and was associated with the retention of viability (70 vs. 55%). The loss of viability of the dried buds was protracted over several days. Ultrastructural examination and vital staining demonstrated cellular and tissue responses to drying. The meristem appeared to withstand drying and 72 h of rehydration whilst the leaf primordia were destroyed immediately after drying. High reactive oxygen species (ROS) activity was associated with bud excision and drying. Caspase-3-like protease activity was detected after rehydration, thereby providing evidence that the dried buds, that had ultimately died, had undergone programmed cell death. ROS production is considered to be the trigger for programmed cell death.

Portulacaria afra, is indigenous to South Africa and has been identified to have several medicinal properties according to traditional knowledge and few studies. The drive around this research is to evaluate the medicinal properties of the leaves, stems and for the first time the roots extracts of Portulacaria afra, using four solvents with different polarities. The aqueous (60°C), methanol, n-hexane and ethyl acetate whole plant extracts of P. afra were investigated for their phytochemical properties, antimicrobial and antioxidant activity. The phytochemical screening revealed that the methanolic and aqueous extracts of the leaves displayed high presence of secondary metabolites compared to n-hexane and ethyl acetate extracts. The methanolic leaves extracts showed strong presence of quinones, phenols, steroid and coumarins while the aqueous leaves extracts contained a moderate presence of saponins, terpenoids, quinones and coumarins. Ethyl acetate leaves extracts revealed a strong presence of tannins, moderate presence of phytosteroids and a low presence of volatile oil. Meanwhile, the leaves extracts with n-hexane showed a considerable amount of saponins with a moderate presence, and a low presence of tannins, volatile oils and terpenoids. The methanolic stems extracts displayed the most significant presence of secondary metabolites, showing a high presence of terpenoids, steroids, phenols and coumarins. The aqueous stems extracts showed a strong presence of glycosides with a moderate presence of saponins. However, ethyl acetate and n-hexane stems extracts displayed a few secondary metabolites with their concentration ranging from medium to low. The ethyl acetate roots extracts displayed a significant elevated amount of quinones with a strong presence. n-hexane roots extracts showed a moderate presence of volatile oil and a low presence of tannins and steroids. Methanolic roots extracts showed a moderate presence of coumarins and glycosides while aqueous roots extracts showed a low presence of glycosides. The overall highest total phenolics contents (TPCs) and total flavonoids contents (TFCs) in all the plant parts, were found to be in the methanol stems extracts and aqueous roots extracts respectively. Next to the methanol leaves and aqueous leaves extracts respectively. However, in the root’s extracts, the aqueous extracts showed the highest total phenolics content while the water extracts had the highest total flavonoids contents. The antimicrobial activities of P. afra whole plant extracts with the various four solvents were tested against three microorganisms Escherichia coli, Staphylococcus aureus and Streptomyces griseus using agar-well diffusion method. The Antimicrobial activity of the n-hexane extracts of the leaves, stems and roots of P. afra presented a wide range of inhibition against all the test microorganisms, ethyl acetate leaves extract showed a considerable effect against Staphylococcus aureus while the methanolic extracts were not active. Aqueous roots extracts demonstrated a strong antimicrobial activity against Staphylococcus aureus while the other extracts were not active. The zones of inhibition ranged from 13 to 24 mm for the plant extracts. The antioxidant activity potential of the aqueous, methanol, n-hexane and ethyl acetate extracts of P. afra leaves, stems and roots extracts were observed through a 2, 2 diphenylpicryhydrazyl (DPPH) free radical assay, hydrogen peroxide scavenging (H₂O₂) and metal chelating activity assay. Ethyl acetate roots extracts exhibited the strongest hydrogen peroxide scavenging activity compared to the other extracts. Meanwhile, aqueous stems extracts showed the highest antioxidant activity against DPPH radical. Aqueous and n-hexane roots extracts displayed the strongest metal chelating ability. These findings reveal the efficacy of the use of several solvents with different polarities for effective and more accurate extraction of various compounds and indicate that the antimicrobial and antioxidant activity of P. afra parts are dependent on the solvent extracts.

Portulacaria afra, is indigenous to South Africa and has been identified to have several medicinal properties according to traditional knowledge and few studies. The drive around this research is to evaluate the medicinal properties of the leaves, stems and for the first time the roots extracts of Portulacaria afra, using four solvents with different polarities. The aqueous (60°C), methanol, n-hexane and ethyl acetate whole plant extracts of P. afra were investigated for their phytochemical properties, antimicrobial and antioxidant activity. The phytochemical screening revealed that the methanolic and aqueous extracts of the leaves displayed high presence of secondary metabolites compared to n-hexane and ethyl acetate extracts. The methanolic leaves extracts showed strong presence of quinones, phenols, steroid and coumarins while the aqueous leaves extracts contained a moderate presence of saponins, terpenoids, quinones and coumarins. Ethyl acetate leaves extracts revealed a strong ...

Bulbine abyssinica is a succulent medicinal plant indigenous to South Africa. The species has been commonly used traditionally by indigenous people for the treatment of various skin related ailments as well as the management of diabetes mellitus. To date, limited studies have been conducted on the underground stems and roots, as well as comparative analyses across the different plant parts of the species. Methanolic extracts of B. abyssinica leaves, underground stems and roots were used to perform phytochemical screening, quantitative phytochemical analyses, antioxidant and antibacterial assays. The leaves contained most of the phytochemical groups tested, as well as higher total phenolic (1841.7 ± 4.8 mg/100g GAE), total flavonoid (809.2 ± 75.6 mg/100g QE), total tannin (2850 ± 70.01 mg/100g GAE) and total proanthocyanidin (636.67 ± 1.67 mg/100g CE) contents compared to the underground stems and roots. The antioxidant activity results showed that the roots exhibited the strongest s...

Abstract Moringa Oleifera commonly known as miracle tree, is widely distributed in tropical and subtropical regions. It is used in traditional medicine to treat several diseases such as diabetes, hypertension, cancer, and other infections. In order to optimize the time of harvesting Moringa plant leaves, it is important to understand how various environmental factors like season affects its chemical composition especially secondary metabolites. Ultra-high-performance liquid chromatography with diode array coupled to electrospray ionization mass spectrometry (UPLC-ESI-QTOFMS) was used for the comprehensive characterization of methanol extract from Moringa Oleifera leaves from different South Africa calendar-based seasons. Some compounds such as Gallic acid, Catechin, Chlorogenic acid, Quercetin, Kaempferol, Quercetin 3,4-diglycoside, Quercetin 3-O-glucoside were quantified. Total phenolic content (TPC), total flavonoid content (TFC) and DPPH scavenging assay were measured as response to the seasonal variations. A total number of 29 Polyphenolic compounds were identified. In overall, trend of Polyphenolic content as a function of the season was as: autumn > winter > summer> spring. The highest level of Gallic acid, Catechin, chlorogenic acid, quercetin, kaempferol, quercetin 3,4-diglycoside, quercetin, TPC and TFC were found in autumn. The lowest EC50 were found in the leaves collected in autumn and winter as an indication of high antioxidant activity as compared to spring and summer. The results from the current study showed a strong evidence that seasonal variation have an impact on the secondary metabolites production. Thus, the best recommended harvesting season is autumn and summer because in winter though gave also high secondary metabolites, there is less biomass during this period.

This Commentary is a response to a Commentary published in the May/June 2020 issue: Nattrass N. Why are black South African students less likely to consider studying biological sciences? S Afr J Sci. 2020;116(5/6), Art. #7864, 2 pages. https://doi.org/10.17159/sajs.2020/7864 Responses to the Commentary in the May/June 2020 issue have been published collectively in a special issue of Volume 116.

In preparation for cryopreservation, Eucalyptus grandis in vitro axillary buds were dried over silica gel. Pretreatment of the buds with 5 mg per L ABA resulted in partial resistance to water loss (0.76 to 0.45 g per g fresh mass basis) as compared with untreated buds (0.76 to 0.33 g per g) and was associated with the retention of viability (70 vs. 55%). The loss of viability of the dried buds was protracted over several days. Ultrastructural examination and vital staining demonstrated cellular and tissue responses to drying. The meristem appeared to withstand drying and 72 h of rehydration whilst the leaf primordia were destroyed immediately after drying. High reactive oxygen species (ROS) activity was associated with bud excision and drying. Caspase-3-like protease activity was detected after rehydration, thereby providing evidence that the dried buds, that had ultimately died, had undergone programmed cell death. ROS production is considered to be the trigger for programmed cell ...

Extreme changes in climate, especially in temperature, could have implications for herbal plants in various world regions. Medicinal plants often produce a wide variety of natural phytochemicals to enhance their defence and survival mechanisms against harsh environmental conditions, and when these mechanisms fail, plants consequently die. We investigated the impact of high temperatures coupled with the specific duration of exposure on the yield and composition of essential oils and trichomes in leaves of Lippia javanica. Plants were exposed to increasing temperatures (25 °C to 47 °C) for different durations (48 h to 144 h). Response surface methodology was applied to assess the interaction between temperature and length of exposure on the essential oil yield, trichome length, and trichome diameter. Essential oils were recovered from the control and treated leaf samples using hydrodistillation and volatile compounds were identified through gas chromatography–mass spectrometry (GC-MS)...