The effect of long-term irrigation using wastewater on heavy metal contents of soils under vegetables in Harare, Zimbabwe

From the Egyptian medicinal plant Polygonum senegalense the fungal endophyte Alternaria sp. was isolated. Extracts of the fungus grown either in liquid culture or on solid rice media exhibited cytotoxic activity when tested in vitro against L5178Y cells. Chromatographic separation of the extracts yielded 15 natural products, out of which seven were new compounds, with both fungal extracts differing considerably with regard to their secondary metabolites. Compounds 1, 2, 3, 6, and 7 showed cytotoxic activity with EC 50 values ranging from 1.7 to 7.8 microg/mL. When analyzed in vitro for their inhibitory potential against 24 different protein kinases, compounds 1- 3, 5- 8, and 15 inhibited several of these enzymes (IC 50 values 0.22-9.8 microg/mL). Interestingly, compounds 1, 3, and 6 were also identified as constituents of an extract derived from healthy leaves of the host plant P. senegalense, thereby indicating that the production of natural products by the endophyte proceeds also under in situ conditions within the plant host.

Cytotoxic metabolites from the fungal endophyte Alternaria sp. and their subsequent detection in its host plant Polygonum senegalense.

Despite the uselfuness of nematicidal compounds in agricultural practices, some serious concerns are raised today about their excessive use leading to enhancement of biodegradation mechanisms in soil expressed as lack of efficacy under field conditions and resistance development. Moreover, the phase-out of methyl bromide has led to the need for a valid alternative to organophosporous and carbamate compounds, such us fosthiazate, fenamiphos, oxamyl, and aldicarb. In the past years, intregated pest management strategies have been practised worldwide to maximize crop production while maintaining and contributing to agriculture sustainability. Biopesticides and specifically bionematicides constitute a desirable component of pest management technology and practices. Particularly, in the frame of our ongoing research on natural nematicides of botanical origin, we have reviewed the international bibliography for candidate nematicidal compounds. We report herein the nematicidal activity of plant metabolites on the basis of their chemical characteristics and structure.

Botanical Nematicides: A Review

Ethnobotanical study of anthelmintic and other medicinal plants traditionally used in Loitoktok district of Kenya

Contamination of leafy vegetables ( Brassica species) by copper (Cu), zinc (Zn), cadmium (Cd), nickel (Ni), lead (Pb) and chromium (Cr), and the subsequent human exposure risks, were determined at two sites in the City of Harare, where wastewater is used for irrigating vegetables. The concentrations of heavy metals (mg kg −1  dry wt.) in vegetable leaves ranged from 1.0 to 3.4 for Cu, 18 to 201 for Zn, 0.7 to 2.4 for Cd, 2.5 to 6.3 for Ni, 0.7 to 5.4 for Pb and 1.5 to 6.6 for Cr. Bio-concentration factors in the range of 0.04–3 were obtained, with Zn and Cd having the highest concentration factors of 1.6 and 3, respectively. Estimated intakes rates of heavy metals from consumption of the vegetables in mg day −1 ranged from 0.04 to 0.05 for Cu, 0.6 to 3.3 for Zn, 0.02 to 0.04 for Cd, 0.05 to 0.1 for Ni, 0.05 to 0.09 for Pb and 0.05 to 0.1 for Cr. Cadmium intake rates were above their recommended minimum risk levels (MRLs) at both sites, while Cu, Ni, Cr and Pb had daily intakes above 40% of their MRLs. Potential health risks, particularly from Cd intake, existed for the daily consumers of the leafy vegetables at both Mukuvisi and Pension sites. Thus, although the practice of growing leafy vegetables using wastewater for irrigation is aimed at producing socio-economic benefits, it is not safe and may not be sustainable in the long-term. There is need for an improved food quality assurance system to ensure that the vegetables comply with existing standards on heavy metal concentrations.

Uptake of heavy metals by vegetables irrigated using wastewater and the subsequent risks in Harare, Zimbabwe

There are several described medicinal plants in Kenya from a flora of approximately 10,000 members. Strong cross-medical information from the 42 ethnic groups points to the high potential of some of these species. The Myrsinaceae are well established ethno-anthelmintics and anti-bacterials. They are harbingers of long alkyl side chain benzoquinones which clearly have a protective function from their histochemical disposition. The main benzoquinone in the sub-family Myrsinodae is embelin while for the Maesodae it is maesaquinone together with its 5-acetyl derivative; the distribution of these benzoquinones by their alkyl side chain length or the presence/absence of a 6-methyl group is in accord with morphological sub-family de-limitation. The benzoquinones showed anti-feedant, anti-microbial, phytotoxic, acaricidal, insecticidal and nematicidal activity. Many other benzoquinones of medium and minor concentration were also isolated and characterised. Some plants belonging to the Polygonaceae which are widely used as ethno-anthelmintics have been studied. The common anthelmintic anthraquinones were obtained from all five Rumex species while the naphthalenic acetogenin derivative, nepodin was more selectively distributed. The leaf of Polygonum senegalense is up to 17% surface exudate; about thirteen non polar flavonoid derivatives (chalcones, dihydrochalcones, flavanones and a flavone) have been isolated from it. From the internal aerial tissues of this plant, the major flavonoids were common flavonoids, quercetin, kaempferol, luteolin and their glycosides. The only unique compound isolated from this plant was 2′-glucosyl-6′-hydroxy-4′-methoxydihydrochalcone whose aglycone, uvangolatin is part of the exudate mixture. Other leaf exudate plants studied include the stomach-ache medicine, Psiadia punctulata (Compositae) from which novel methylated flavonoids, kaurene and trachyloban diterpenes have been found.

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Bioactive compounds from some Kenyan ethnomedicinal plants: Myrsinaceae, Polygonaceae and Psiadia punctulata

Diterpenes from the leaf exudate of Psiadia punctulata

Bull. Chem. Soc. Ethiop. 1993, 7(1) 1-10. Bull. Chem. Soc. Ethiop. 1993, 7(1) 1-10 Bull. Chem. Soc. Ethiop. 1993, 7(1) 1-10

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Biembelin - a new symmetrical bisbenzoquinone from Rapanea Melanphloes

Two new natural benzoquinones, 2,5-dihydroxy-3-methyl-6-undecyl-1,4-benzoquinone (1, muketanin) and 2-O-methyl-muketanin (2) have been isolated from fruits of Myrsine africana and Maesa lanceolata respectively.

New Dialkyl Benzoquinones from Fruits of Myrsine africana L and Maesa lanceolata, Forsk

Laboratory studies were conducted to assess the toxicity and growth-inhibitory activity against Aedes aegypti larvae, of the crude acetone extracts of Polygonum senegalense (Meissn.) leaves, itsflavonoid component 2′,6′-dihydroxy-4′-methoxydihydrochalcone and the internal tissue flavanol quercetin. The first two showed significantly high insecticidal and growth-inhibitory activity even at low concentrations, whereas quercetin was toxic only at concentrations above 7μg/ml.

J. Ogweno Midiwo

Papers

Bioactive compounds from some Kenyan ethnomedicinal plants: Myrsinaceae, Polygonaceae and Psiadia punctulata

Diterpenes from the leaf exudate of Psiadia punctulata

Biembelin - a new symmetrical bisbenzoquinone from Rapanea Melanphloes

New Dialkyl Benzoquinones from Fruits of Myrsine africana L and Maesa lanceolata, Forsk

Toxicity and growth-inhibitory activity of Polygonum senegalense (Meissn.) surface exudate against Aedes aegypti larvae