Browsing by Author "Dakora, Felix D"

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    Open Access
    Characterization of XV7 and XV9 cDNA clones which confer osmotolerance to Eschericia coli
    (1998) Salie, S; Dakora, Felix D
    The sequence similarity between XV7 and the mammalian syntaxin-like protein kinase receptor shows that XV7 may function similar to that of animal protein kinases. The syntaxin-like protein kinase receptor was recently entered into the Genbank (Thoreau, unpublished), therefore not much is known about its characteristics. It does show similarity to a myotonin protein kinase, MtPK (Thoreau, unpublished). The plant receptor-like protein kinases (RLKs) are structurally related to the polypeptide growth factor receptors of animals (Walker, 1994). Although several ABA and stressresponsive gene have been characterised, their physiological role in the initial perception and transduction of stress signals is not well defined Recent reports suggest that characterising phosphorylation/ dephosphorylation responses and investigation of stress-responsive protein kinases may contribute towards identifying the pivotal regulatory steps in plant responses to environmental stress.
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    Ecology of the (Brady)rhizobium symbiotic relationship with Fabaceae in the south-western Cape
    (1996) Marumo, Moscow; Stock, WD; Dakora, Felix D
    The mediterranean ecosystems of the south-western Cape, South Africa occur mainly on nutrient-poor acid sands and less often on limestone and mixed limestone soil types which support a high species diversity of Fabaceae. This species richness and diversity is suggested to be a result of a high incidence of microsymbiont/host specificity among the fynbos Fabaceae (Cowling et al. 1990). This hypothesis by Cowling et al. (1990) has ignored other factors which may possibly play a major role in microsymbiont/host relationships in the Cape Floristic Region, such as soil conditions, and bacterial strain competition which may also influence patterns of nodulation in the region. Cowling et al.'s (1990) hypothesis was speculative and was without any experimental basis. In this thesis investigations were carried out to assess the applicability of this hypothesis to fynbos, while at the same time other factors that could affect the microsymbiont/host relationship in fynbos were investigated. In order to test Cowling et al.'s (1990) hypothesis, various complementary methods were used to assess the nodulation patterns of several indigenous fynbos species. Extracts from a range of soils differing in chemical and physical properties were used to inoculate test species, and their nodulation parameters observed. However, a second more specific approach was used to confirm the results of the previous study. This method involved cross-inoculation of indigenous test species used in the previous study with nodule homogenates prepared from other fynbos species originating from various sites within the Cape Floristic Region.
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    Effects of seaweed concentrate (Kelpak) on nitrogen fixation of cowpea (Vigna ungulata L. Walp.) and soybean (Glycine max L. Merr.) and on the growth of their rhizobial symbionts (Bradyrhizobium strain CB756 and Bradyrhizobium japonicum strain CB1809)
    (2001) Leitao, Daniela; Dakora, Felix D
    Seaweed extracts are known to have a stimulatory effect on the growth and development of plants. This study investigated the effect of applying a commercial seaweed concentrate (kelpak) on rhizobia growth (Bradyrhizobium strain CB756 and Bradyrhizobium japonicum strain CB 1809) and nitrogen fixation in cowpea ( Vigna ungulata L. Walp.) and soybean (Glycine ma.x L. Merr.) plants. Two concentrations of Kelpak (1:100 v/v and 1:500 v/v seaweed concentrate dilutions) were applied to pots with seeds or seedlings at sowing and after every 14 days (1:l00A; 1:500A), at sowing and after every 7 days (1:100B; 1:500B) or after germination and after every 14 days (1: l00C; 1:500C). From the first experiment, cowpea plants in the various treatments showed no change in shoot biomass. The root biomass was significantly inhibited in treatment 1:100B relative to the control. The nodule dry matter of cowpea was reduced in 1:100A, 1:100B and 1:100C Kelpak concentrations compared to control, with a significant increase only in 1:100B Kelpak concentration. As a result, cowpea plants showed the highest total biomass in 1:500B treatment. Although shoot N in cowpea plants remained unchanged under the various kelpak treatments, root N was significantly reduced. Soybean plants showed a significant decrease in shoot and root biomass compared to the control. Nodule dry matter was lowest for soybean plants in Kelpak treatments 1:500B, 1:100B and 1:100C. As a result, there was a decrease in soybean total growth in treatment 1:500B compared to the control. Total N in shoots and roots was highest in soybean plants growing in 1:500A relative to the control. Culturing cells of Bradyrhizobium strain CB756 with Kelpak showed a significant increase in growth at 1:100 and 1:500 dilutions compared to the control. However, over the 93 h period with sterile Kelpak culture there was an inhibition in growth of strain CB756 relative to the control. Beyond the 93 h there was a significant increase in growth of Bradyrhizobium japonicum strain CB 1809 in all Kelpak treatments. The 1:100 concentration showed the highest bacterial growth compared to the control and the other treatments. These data suggests the presence of an active molecule in Kelpak that stimulates rhizobial growth and its symbiotic interaction with legumes.
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    Effects of ultraviolet-B radiation on plant growth, symbiotic function and concentration of metabolites in legumes and an assessment of F1 generation for carryover effects
    (2003) Chimphango, Samson; Dakora, Felix D
    Reduction in ozone layer thickness in the stratosphere and the resultant increase in ground level of biologically active ultraviolet-B (UV-B) radiation prompted research into the effect of UV-B on growth and metabolism of terrestrial plants. In this study, eight legume species including three tropical food grain legumes [Vigna unguiculata (L.) Walp. (cowpea), Glycine max (L.) Merr (soybean), and Phaseolus vulgaris (L.) (common bean)], two temperate pasture legumes [Lupinus luteus (lupin) and Vicia atropurpurea (vetch)], a tree [Virgilia oroboides (Bergius T.M. Salter] and two shrub legumes [Cyclopia maculata (L.) Vent (honey bush) and Podalyria calyptrata Willd] indigenous to Southern Africa were exposed to UV-B radiation at above and below-ambient levels, and assessed for its effects on plant growth, symbiotic function and root concentration of metabolites.
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    Marama bean (Tylosema esculentum), a non-nodulating high protein legume indigenous to the Kalahari sands : studies of its N nutrition
    (2004) Thomas, Theopolina; Dakora, Felix D
    Marama bean is a non-nodulating perennial legume native to the nutrient-poor soils of the Kalahari Sands. In Botswana and Namibia, it is the staple food of the Khoisan people. Marama bean, however, still have not been cultivated or established as an agricultural crop in these countries. This study investigated soil factors affecting the distribution and growth of marama bean in the field and how it would respond to additional N and P supply both under field and glasshouse conditions. The study then attempts to explore and understand the mechanisms employed by marama bean to acquire high nutrient concentration in its organs.
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    N2 fixation and rhizosphere ecology of aspalathus linearis subsp. linearis(rooibos tea)
    (1997) Muofhe, Mmboneni Leonard; Dakora, Felix D
    Aspalathus linearis subsp. linearis grows in acid sands of the Cedarberg with pH ranging from 3.8-5.5. Under these conditions:, some essential nutrients are likely to be limiting. In this study, the response of Aspalathus linearis subsp. linearis to N, P, Ca and B was investigated I under field and glasshouse conditions to determine whether provision of supplemental mineral nutrients promotes growth and N2 fixation for increased tea production, and whether this legume from low nutrient environment responds to fertilization. Interestingly, provision of N and P stimulated plant growth and symbiotic performance under field and glasshouse conditions. However, like most legumes, there was sensitivity to high levels of N which resulted in a decline in nodulation and N2 fixation. Unlike P and N nutrition, Ca supply led to a significant decrease in symbiotic performance of the legume under both glasshouse and field conditions. The amounts of N fixed ranged from 50 to 225 mg N/plant under glasshouse conditions and 3.8 to 7.1 g N/plant in the field. When inoculated with soils collected from different areas outside the Cedarberg, Aspalathus linearis subsp. linearis failed to nodulate, suggesting the possible absence of specific bradyrhizobia which nodulate this legume.
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    N₂ fixation, plant mineral nutrition and C metabolites in cowpea/maize cropping systems
    (2002) Monakisi, Charlotte; Dakora, Felix D
    The objective of this study was (1) quantify N₂ fixation in sole and mixed cropped cowpea, (2) To access nutrient assimilation by component species in the cropping system, and (3) to determine the effects of cropping system on C metabolites. At harvest the dry mass of both cowpea and maize were highest in sole crops. There was a significant difference in % nitrogen of maize and cowpea plants from the different cropping systems. Total nitrogen content was highest in sole cropped maize and cowpea plants with sole cowpea fixing the most N₂. δ¹⁵N values were lower for the shoots of symbiotic cowpea compared to the maize. Root δ¹⁵N values were also generally lower in cowpea than in maize. The %N derived from fixation (Ndfa) was similar for sole, intra and intercropped cowpea. However the amount of N fixed was significantly greater in sole cowpea compared to intra- and intercropped cowpea. When nutrient uptake and assimilation was assessed in the cropping system, it was found that mineral elements such as Ca, Mg, Cu, Zn and B occurred in significantly greater concentrations in the N₂-fixing legume compared to the cereal partner. However the concentration of soluble sugars and starch remained the same for both shoot and roots of cowpea and maize plants in the cropping system.
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    Potential use of rhizobial bacteria as promoters of plant growth for increased yield in landraces of African cereal crops
    (2004) Matiru, Viviene N; Dakora, Felix D
    Rhizobia form root nodules that fix nitrogen (N2) in symbiotic legumes. Extending the ability of these bacteria to fix N2 in non-legumes such as cereals would be a useful technology for increased crop yields among resource-poor farmers. Although some inoculation attempts have resulted in nodule formation in cereal plants, there was no evidence of N2 fixation. However, because rhizobia naturally produce molecules (auxins, cytokinins, abscicic acids, lumichrome, rhiboflavin, lipo-chito-oligosaccharides and vitamins) that promote plant growth, their colonization and infection of cereal roots would be expected to increase plant development, and grain yield. We have used light, scanning, and transmission electron microscopy to show that roots of sorghum and millet landraces from Africa were easily infected by rhizobial isolates from five unrelated legume genera. With sorghum, in particular, plant growth and phosphorus (P) uptake were significantly increased by rhizobial inoculation, suggesting that field selection of suitable rhizobia/cereal combinations could increase yields and produce fodder for livestock production.
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    Subcellular organization of N2-fixing nodules of cowpea (Vigna unguiculata) supplied with silicon.
    (Springer, 2001) Nelwamondo, Azwianewi; Jaffer, Mohamed A; Dakora, Felix D
    Provision of silicon (0, 0.048, 0.096, 0.24, 0.48, and 0.96 g/1) in the form of silicic acid (H4SiO4) to nodulated cowpea plants(Vignia unguiculata [L.] Walp.) grown in liquid culture resulted in considerable changes in the internal organization of nodule structure. Compared to the control plants which received no added silicate, bacteroid numbers increased significantly (P ≤ 0.05) at silicate concentrations of both 0.096 and 0.48 g/1. The number of symbiosomes also increased by 3.2-fold at the silicate concentration of 0.96 g/1 compared to the control. In contrast, the size of bacteroids and symbiosomes decreased significantly (P ≤ 0.05) inside nodules of silicate-treated plants. The peribacteroid space was also decreased considerably (P ≤ 0.05) with the application of 0.096 and 0.96 g of silicate per liter to plants. However, the size of intercellular spaces adjacent to infected and uninfected interstitial cells within the nodule medulla increased significantly (P ≤ 0.05) at 0.096 g of silicate per liter followed by a sharply marked (P ≤ 0.05) decrease with each subsequent increase in silicate application. The result was a large decrease (P≤0.05) in the area of bacteria-infected tissue occupied by intercellular space at the highest silicate concentration, which was caused by a significant (P ≤ 0.05) increase in cell wall thickness. Our findings show that the positive effects of silicon on N2 fixation might actually be due to an increased number of bacteroids and symbiosomes.
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    The symbiotic interaction of Bradyrhizobium japonicum with bambara groundnut and cowpea and the effects of NOD gene-inducers, daidzein and genistein
    (1998) Salie, S; Dakora, Felix D
    The aim of this project was to investigate whether nodulation, and nitrogen concentration of legumes can be increased by providing additional nod geneinducer compounds. Both daidzein and genistein are nod gene-inducers for rhizobia nodulating cowpea, bambara groundnut, soybean and the common bean.
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    Symbiotic N² fixation in cyclopia vent. spp. (honeybush) : towards sustainable cultivation in the Western Cape of South Africa
    (2004) Spriggs, Amy Clare; Dakora, Felix D
    An indigenous cash crop, called honeybush (Cyclopia spp., Fabaceae), has recently gained popularity in the Western Cape of South Africa and its potential for cultivation is being investigated. The crop is an N²-fixing legume and its yields would therefore be improved by enhancing its N²-fixing capacity. This would allow increased tea yields without the need for chemical fertilizers, promoting the crop's status as an organically farmed health product, limiting the environmental degradation associated with N fertilizer use and benefiting small-scale farmers in the region who cannot afford chemical fertilizers.