Bhekumthetho Ncube

ABSTRACT The polyphenolic content and antimicrobial activity of 1-year-old ex vitro-acclimatized plant samples of the endangered plant species Merwilla plumbea were evaluated. Acclimatized plants were derived from in vitro media containing different supplements. Spectrophotometric techniques and micro-dilution assays for the determination of polyphenols and antimicrobial activities, respectively, were used. Significantly higher levels of total phenols, flavonoids, and proanthocyanidins were recorded in the greenhouse-acclimatized plants compared to the in vitro-derived samples. In contrast with the untreated field-grown plants, the levels of these compounds in both in vitro-derived and ex vitro-acclimatized plants yielded multiple-fold increases. The highest levels of flavonoids were obtained in ex vitro plants treated with 200 mg l−1 yeast malt broth (YMB), 0.45 μM thidiazuron (TDZ), and 0.054 μM naphthaleneacetic acid (NAA). The same treatment also exhibited good antimicrobial activity, an attribute that might suggest the involvement of these compounds in the observed bioactivity. The fact that Murashige and Skoog (MS) medium supplemented with organic elicitors differentially affected the accumulated levels of polyphenols in vitro, and their subsequent carry-over and higher expression in an ex vitro environment over time, makes the technology an attractive system for commercial multiplication and cultivation of medicinal plants.

Cyrtanthus (Amaryllidaceae) is a genus of perennial geophytes, endemic to the southern African region. Destructive and indiscriminate harvesting of bulbs for medicinal and ornamental purposes has led to intensive decimation of the populations of most of these species in their natural habitats. The aim of this study was to develop in vitro regeneration systems for Cyrtanthus contractus, Cyrtanthus guthrieae, and Cyrtanthus obliquus using twin-scale explants from mature bulbs. Twin scales from the three species were cultured on solid Murashige and Skoog (MS) medium with different concentrations of 6-benzyladenine (BA) and α-naphthaleneacetic acid (NAA) under 16/8-h light/dark conditions at 25 ± 2°C. The best shoot induction responses were obtained on MS medium containing 4.4 μM BA + 1.1 μM NAA (3.1 shoots/explant) for C. contractus and C. guthrieae and 6.7 μM BA + 2.7 μM NAA for C. obliquus. When the best shoot induction medium for each species was investigated for the effect of cytok...

ABSTRACT Indigenous leafy vegetables possess high horticultural potential based on their long utilisation history by local communities across Africa. Phytochemical and antioxidant properties of 50% aqueous methanol and water extracts of three indigenous as well as two commercial leafy vegetables commonly consumed in southern Africa were evaluated. The total extractable phenolic content was highest for Amarathus dubius (5.16 ± 0.12 mg GAE/g DW) followed by Cleome gynandra (3.94 ± 0.09 mg GAE/g DW). Total flavonoid concentration was highest for A. dubius (3.89 ± 0.28 mg CE/g DW) followed by C. gynandra (2.19 ± 0.11 mg CE/g DW) and Cucurbita maxima (1.55 ± 0.04 mg CE/g DW). No proanthocyanidins were detected in C. maxima and Brassica napus cv Covo whereas low concentrations were recorded in other vegetables. Total saponins were variable across the evaluated extracts, with the highest concentrations recorded for B. napus cv Covo (83.2 ± 16.58 mg DE/g DW). Total iridoid content was highest for C. gynandra (9.14 ± 0.20 mg HE/g DW). More potent DPPH radical scavenging activities were exhibited by 50% aqueous methanol extracts compared to water extracts. A similar trend was observed in the ferric-reducing antioxidant power assay. The antioxidant activity based on the rate of β-carotene bleaching was higher for water extracts compared to 50% aqueous methanol extracts. The indigenous vegetables evaluated in this study had higher levels of phytochemicals and also exhibited more potent antioxidant activity compared to the commercial varieties. These findings not only suggest the importance of the indigenous vegetables in a healthy diet, but also provide a motivation for exploring their horticultural potential.