Long-term population studies and the development of an integrated management programme for control of Opuntia stricta in Kruger National Park, South Africa

1. A cactus, Opuntia stricta , has invaded almost 16 000 ha of conserved, natural habitatand has become a major weed problem in Kruger National Park (KNP), South Africa.
2. The main objectives in the control of O. stricta are to reduce the density of the weed and to curb long-range dispersal of seeds by preventing young plants from reaching the size (28 cladodes) at which they start to produce fruits.
3. Herbicides have failed to provide satisfactory control of O. stricta because the weed infestations are replenished from seeds in the soil and from small plants that are overlooked during spraying.
4. A phycitid moth, Cactoblastis cactorum , was released in KNP during 1988 in an attempt to control O. stricta biologically.
5. Population counts of the biological control agent and of the weed over a 5-year period showed that, even though C. cactorum has not provided complete control of O. stricta in KNP, the moderate levels of larval damage have stunted the growth of O. stricta and have considerably extended the time that the young plants take to reach sexual maturity.
6. Comparisons of modelled (i.e. with no C. cactorum ) and actual populations of O. stricta showed that C. cactorum is making a substantial contribution to the control of O. stricta in residual infestations of the weed that have been treated with herbicides.
7. The need for long-term evaluation studies in biological weed control is demon strated by the development of an integrated management programme for effective control of O. stricta .     

Edaphic Distribution of Some Species of the Fern Genus Adiantum in Western Amazonia1

The distribution patterns of Adiantum species were inventoried at twelve noninundated rain forest (tierra firme) sites in Amazonian Peru and Ecuador. Six species belonging to the genus were found, and four of these were abundant at some of the sites. At six of the sites none of the species was particularly abundant. Both the occurrence and the abundance of the species varied among sites with regard to soil texture and concentration of exchangeable bases and within sites with regard to topography. Adiantum tomentosum) Klotzsch was restricted to loamy soils with intermediate to low content of extractable bases and was locally most abundant in the well drained parts of slopes and ridge tops. Adiantum terminatum Kunze ex Miq. and A. humile Kunze occurred at sites with intermediate to high content of extractable bases, but their relative abundances differed among and within sites. Adiantum pulverulentum L. was restricted to soils with relatively high base concentration. Ecological differences among the species obviously explained many of the differences in their distribution patterns at the local and regional scales, and may be important for the understanding of such patterns at biogeographical scales as well.     

Cytokinesis and Midzone Microtubule Organization in Caenorhabditis elegans Require the Kinesin-like Protein ZEN-4

Members of the MKLP1 subfamily of kinesin motor proteins localize to the equatorial region of the spindle midzone and are capable of bundling antiparallel microtubules in vitro. Despite these intriguing characteristics, it is unclear what role these kinesins play in dividing cells, particularly within the context of a developing embryo. Here, we report the identification of a null allele of zen-4, an MKLP1 homologue in the nematode Caenorhabditis elegans, and demonstrate that ZEN-4 is essential for cytokinesis. Embryos deprived of ZEN-4 form multinucleate single-celled embryos as they continue to cycle through mitosis but fail to complete cell division. Initiation of the cytokinetic furrow occurs at the normal time and place, but furrow propagation halts prematurely. Time-lapse recordings and microtubule staining reveal that the cytokinesis defect is preceded by the dissociation of the midzone microtubules. We show that ZEN-4 protein localizes to the spindle midzone during anaphase and persists at the midbody region throughout cytokinesis. We propose that ZEN-4 directly cross-links the midzone microtubules and suggest that these microtubules are required for the completion of cytokinesis.     

Purification and characterization of cyclodextrin β-glucanotransferase from novel alkalophilic bacilli

The discovery of novel bacterial cyclodextrin glucanotransferase (CGTase) enzyme could provide advantages in terms of its production and relative activity. In this study, eight bacterial strains isolated from soils of a biodiversity-rich vegetation in Egypt based on their hydrolyzing activity of starch, were screened for CGTase activity, where the most active strain was identified as Bacillus lehensis. Optimization process revealed that the using of rice starch (25 %) and a mixture of peptone/yeast extract (1 %) at pH 10.5 and 37 °C for 24 h improved the bacterial growth and enzyme activity. The bacterial CGTase was successively purified by acetone precipitation, gel filtration chromatography in a Sephadex G-100 column and ion exchange chromatography in a DEAE-cellulose column. The specific activity of the CGTase was increased approximately 274-fold, from 0.21 U/mg protein in crude broth to 57.7 U/mg protein after applying the DEAE-cellulose column chromatography. SDS-PAGE showed that the purified CGTase was homogeneous with a molecular weight of 74.1 kDa. Characterization of the enzyme exhibited optimum pH and temperature of 7 and 60 °C, respectively. CGTase relative activity was strongly inhibited by Mg²⁺, Zn²⁺, Al³⁺ and K⁺, while it was slightly enhanced by 5 and 9 % with Cu²⁺ and Fe²⁺ metal ions, respectively.     

Abacavir-Reactive Memory T Cells Are Present in Drug Na?ve Individuals

BackgroundFifty-five percent of individuals with HLA-B*57:01 exposed to the antiretroviral drug abacavir develop a hypersensitivity reaction (HSR) that has been attributed to naïve T-cell responses to neo-antigen generated by the drug. Immunologically confirmed abacavir HSR can manifest clinically in less than 48 hours following first exposure suggesting that, at least in some cases, abacavir HSR is due to re-stimulation of a pre-existing memory T-cell population rather than priming of a high frequency naïve T-cell population.MethodsTo determine whether a pre-existing abacavir reactive memory T-cell population contributes to early abacavir HSR symptoms, we studied the abacavir specific naïve or memory T-cell response using HLA-B*57:01 positive HSR patients or healthy controls using ELISpot assay, intra-cellular cytokine staining and tetramer labelling.ResultsAbacavir reactive CD8+ T-cell responses were detected in vitro in one hundred percent of abacavir unexposed HLA-B*57:01 positive healthy donors. Abacavir-specific CD8+ T cells from such donors can be expanded from sorted memory, and sorted naïve, CD8+ T cells without need for autologous CD4+ T cells.ConclusionsWe propose that these pre-existing abacavir-reactive memory CD8+ T-cell responses must have been primed by earlier exposure to another foreign antigen and that these T cells cross-react with an abacavir-HLA-B*57:01-endogenous peptide ligand complex, in keeping with the model of heterologous immunity proposed in transplant rejection.     

A Quantitative Model of the GIRK1/2 Channel Reveals That Its Basal and Evoked Activities Are Controlled by Unequal Stoichiometry of Gα and Gβγ

G protein-gated K⁺ channels (GIRK; Kir3), activated by Gβγ subunits derived from G_i/o proteins, regulate heartbeat and neuronal excitability and plasticity. Both neurotransmitter-evoked (I_evoked) and neurotransmitter-independent basal (I_basal) GIRK activities are physiologically important, but mechanisms of I_basal and its relation to I_evoked are unclear. We have previously shown for heterologously expressed neuronal GIRK1/2, and now show for native GIRK in hippocampal neurons, that I_basal and I_evoked are interrelated: the extent of activation by neurotransmitter (activation index, R_a) is inversely related to I_basal. To unveil the underlying mechanisms, we have developed a quantitative model of GIRK1/2 function. We characterized single-channel and macroscopic GIRK1/2 currents, and surface densities of GIRK1/2 and Gβγ expressed in Xenopus oocytes. Based on experimental results, we constructed a mathematical model of GIRK1/2 activity under steady-state conditions before and after activation by neurotransmitter. Our model accurately recapitulates I_basal and I_evoked in Xenopus oocytes, HEK293 cells and hippocampal neurons; correctly predicts the dose-dependent activation of GIRK1/2 by coexpressed Gβγ and fully accounts for the inverse I_basal-R_a correlation. Modeling indicates that, under all conditions and at different channel expression levels, between 3 and 4 Gβγ dimers are available for each GIRK1/2 channel. In contrast, available Gα_i/o decreases from ~2 to less than one Gα per channel as GIRK1/2''s density increases. The persistent Gβγ/channel (but not Gα/channel) ratio support a strong association of GIRK1/2 with Gβγ, consistent with recruitment to the cell surface of Gβγ, but not Gα, by GIRK1/2. Our analysis suggests a maximal stoichiometry of 4 Gβγ but only 2 Gα_i/o per one GIRK1/2 channel. The unique, unequal association of GIRK1/2 with G protein subunits, and the cooperative nature of GIRK gating by Gβγ, underlie the complex pattern of basal and agonist-evoked activities and allow GIRK1/2 to act as a sensitive bidirectional detector of both Gβγ and Gα.