15 research outputs found

    Taxanes convert regions of perturbed microtubule growth into rescue sites

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    Microtubules are polymers of tubulin dimers, and conformational transitions in the microtubule lattice drive microtubule dynamic instability and affect various aspects of microtubule function. The exact nature of these transitions and their modulation by anti -cancer drugs such as Taxol and epothilone, which can stabilize microtubules but also perturb their growth, are poorly understood. Here, we directly visualize the action of fluorescent Taxol and epothilone derivatives and show that microtubules can transition to a state that triggers cooperative drug binding to form regions with altered lattice conformation. Such regions emerge at growing microtubule ends that are in a pre-catastrophe state and inhibit microtubule growth and shortening. Electron microscopy and in vitro dynamics data indicate that taxane accumulation zones represent incomplete tubes that can persist, incorporate tubulin dimers and repeatedly induce microtubule rescues. Thus, taxanes modulate the material properties of microtubules by converting destabilized growing microtubule ends into regions resistant to depolymerization

    Studies on stem cuttings of kiwi (Actinidia chinensis PL. CV Bruno)

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    The work was carried out to study the effects of some auxins and boron in the rooting of kiwi (Actinidia chinensis Planch cv Bruno) stem cuttings.. These cuttings were treated on the base individually with H2O; NAA 300 mg.L-1; IBA 300 mg.L-1; NAA 300 mg.L-1 + Boron; IBA 300 mg.L-1 + Boron; NAA 0,5%-talc and IBA 0,5%-talc. After the treatments, the cuttings were placed in styrofoam trays with vermiculite under moist conditions for 120 days. The evaluation of auxin and boric acid effects were made by observing rooted stem cuttings percentage; reducing and total sugar analysis (g/100 g of dry matter); and tryptophan analysis (in µg/100 mg of dry matter). The effects of such treatments were observed during four seasons of the year. The results showed that summer season was the best for rooting. Use of IBA or NAA in the cuttings showed to be unnecessary.<br>O presente trabalho teve como objetivo, estudar o efeito de auxinas sintéticas e do boro, sobre o enraizamento de estacas caulinares de kiwi (Actinidia chinensisPlanch. cv Bruno). As estacas continham dois nós com aproximadamente 10 cm de comprimento, contendo 2 folhas cortadas ao meio. As bases das estacas receberam os seguintes tratamentos: control (H2O); NAA 300 mg.L-1; IBA 300 mg.L-1; NAA 300 mg.L-1 + B; IBA 300 mg.L-1 + B; NAA 0,5%-pó e IBA 0,5%-pó. Após os tratamentos as estacas foram plantadas em bandejas de enraizamento contendo vermiculita pura e colocadas em câmara de nebulização por 120 dias até a coleta das mesmas. Para a avaliação do efeito das auxinas e boro, foram realizadas as seguintes observações: 1. porcentagem de estacas enraizadas; 2. análise de açúcares redutores e açúcares totais (em g/100 g de matéria seca); 3. análise de triptofano (em µg/100 mg de matéria seca). Além disso, foram verificados o efeito dos tratamentos em quatro épocas, que corresponderam às estações do ano (primavera, verão, outono e inverno). Através dos resultados obtidos no processo de enraizamento de estacas caulinares de kiwi (Actinidia chinensis Planch. cv Bruno), conclui-se ser o verão a melhor época de coleta dos ramos para a produção das estacas sem a necessidade do tratamento com auxinas
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