Medicinal properties and micropropagation of Cussonia species.
Cussonia species (commonly known as Cabbage trees) are indigenous to South Africa and are used in traditional medicine to treat an assortment of diseases. Due to their attractive growth form, they are assets in gardens. However, there are no developed methods for propagating these species. The use of three selected species, Cussonia paniculata (Eckl. & Zeyh.), C. spicata (Thunb.) and Schefflera umbellifera (Sond.) Baill, = C. umbellifera), in traditional medicine was validated. Rapid propagation protocols for C. paniculata and C. spicata were investigated and ultimately developed for the former species. Cussonia paniculata, C. spicata and C. umbellifera were screened for their medicinal properties, mainly focussing on anti-bacterial, anti-inflammatory and anti-malarial activities. In the anti-bacterial screening, C. spicata bark and root extracts showed activity against selected Gram-positive and Gram-negative bacterial strains at a concentration of 50 mg ml ¯¹ . The highest inhibition was observed with ethanol and ethyl acetate root extracts against Staphylococcus aureus. The other two species did not show anti-bacterial activity. Ethanol and ethyl acetate extracts of all species showed anti-inflammatory activity in the cyclooxygenase assay (COX-1) at a concentration of 8 μg ml ¯¹, These active extracts showed an inhibition percentage that was greater than 50 % against cyclooxygenase. In the anti-malarial screening , bark extracts were screened. C. umbellifera bark extracts exhibited the best inhibition against P. falciparum, a malaria-causing agent in humans. The percentage inhibition of these extracts was up to 100% at a concentration of 200 μg ml ¯¹ . While C. spicata is known to be used to treat malaria, the screening results showed much less activity (less than or equal to 35 %) as compared to C. umbellifera, which is preferably used to treat malaria. The results obtained from screening these three species validated their use in traditional medicine. This means that the people or traditional healers use these species for different treatments by possibly relying on past knowledge about the effects after administering the medicine. Fingerprinting using Thin Layer Chromatography (TLC) was used in an attempt to determine whether there are any chemical differences or similarities between the three species. There were similarities between the plant parts across the species as well as some differences. However, this method cannot be used as an unequivocal test to deduce that compounds that are present in a certain species and not in others are the ones responsible for bringing about a certain biological activity. That can only be achieved by a bioassay-guided isolation of possible compounds. A tissue culture protocol was developed to produce a large -number of plants of C. paniculata. Explants were derived from nodal explants of in vitro germinated seeds and cultured on Murashige and Skoog (MS) (1962) medium supplemented with 3% sucrose, 2.5 mg l ¯¹ BA and solidified with 3 g l ¯¹ Gelrite. These explants produced multiple shoots. The average number of shoots per explant ranged between 1 to 3.5. Multishoots were subcultured on to rooting media and roots were produced on MS with 0.75 mg l ¯¹ IBA and 1 mg l ¯¹ NAA. Callus from zygotic embryos also produced plantlets on MS supplemented with 1.5 mg l ¯¹ 2,4-D and 0.5 mg l ¯¹ BA. Hyperhydricity was encountered in this study. This problem was reversed successfully by transferring the shoots from medium solidified with 3 g l ¯¹ Gelrite to medium solidified with 8 g l ¯¹ agar. Plantlets were successfully acclimatized for planting ex vitro. The percentage of healthy plants after a 35-day acclimatization period was 63 %. C. spicata was not successfully micropropagated from shoot-tip explants. However, a protocol was developed for decontaminating shoot-tips from the mother plants. The plant material was successfully decontaminated with 0.01% HgCl₂ for 15 min. The decontamination percentage was up to 80 %. Browning of the explants was observed and it was successfully treated with soaking the explants in a 15 mg l ¯¹ ascorbic acid solution for 15 min. A high percentage of shoot-tip regeneration (80 %) was observed when they were cultured on MS medium supplemented with 2 mg l ¯¹ BA, 1 mg l ¯¹ IAA and 1 mg l ¯¹ GA₃. However, multishoots were not observed as in C. panicualata. Shoot elongation in vitro was similar to shoot elongation as it occurs in nature. The shoots elongated and a flush of palmitately arranged leaves were produced. Further research is required to investigate a commercially viable protocol for rapid propagation and conservation of the germplasm of Cussonia species.