Superexpressão do gene dehidrina de Arachis duranensis em plantas transgênicas de Arabidopsis thaliana

Dissertação (mestrado)—Universidade de Brasília, Departamento de Botânica, Programa de Pós-Graduação em Botânica, 2016.

Effects of nitrogen level on purslane antioxidant activity.

The high antioxidant activity of purslane, Portulaca oleracea L., gives it a high nutritional and functional value. The commercial production of purslane has increased in Portugal, making it necessary to know the effects of inputs, mainly nitrogen, on the antioxidant activity. The main goal of this study was to evaluate the influence of nitrogen application on purslane antioxidant activity. The experiment was carried out with for treatments: 30, 60 and 90 kg/ha of nitrogen. Plants of golden-leaf purslane were grown in Styrofoam-boxes filled with substrate and fertigated two times per week, over four weeks with ammonium nitrate solution (16.9% NO3-N and 16.7 NH4+-N). The increase in the nitrogen level decreased the water-soluble proteins content. However the ascorbate, phenols content as well as antioxidant activity measured by FRAP method was not affected by nitrogen level. Plants shoot antioxidant activity, measured by DPPH method decreased significantly in the treatment with 90 kg N/ha (26.20 g/g gallic acid). On the other hand, plant shoot antioxidant activity mediated by peroxidases was higher in treatment 30 kg N/ha (0.459 µmol min-1/mg prot.). Application of 60 kg N/ha allowed a vigorous plant growth without disturb its antioxidants and conservation properties.

Fitoextracção de cádmio de solos contaminados, com plantas seleccionadas

A remediação de locais contaminados com metais pesados usando plantas hiperacumuladoras aparenta ser uma alternativa bastante viável. Neste trabalho comparou-se a acumulação e tolerância ao cádmio (Cd), ambas baseadas nas respostas ao stress oxidativo em três espécies de plantas diferentes: Brassica juncea (L.) Czem., Nicotiana tabacum L. e Solanum nigrum L., descritas na literatura como plantas bastante tolerantes ou até com características híper acumuladoras. As plantas cresceram num solo contaminado com diferentes concentrações de Cd (O- 35 mg kg-1) durante um período de 90 dias. O factor de translocação (FT), utilizado para medir a translocação efectiva do Cd da raiz para a parte aérea, variou consideravelmente entre as espécies desenvolvidas. A N. tabacum foi a planta que apresentou os maiores valores de FT. Neste trabalho foi a única planta que preencheu todas as condições para ser considerada hiperacumuladora para todos os níveis de contaminação do solo. Por outro lado, a S. nigrum apresentou os maiores valores de concentração de Cd nos tecidos, com um FT > 1, na presença de 5 mg Cd kg·1 de solo. Apesar da B. juncea ter apresentado um resultado de FT inferior às restantes, foi a única planta com valores crescentes de FT com o aumento da contaminação de Cd. O stress oxidativo nas plantas desenvolvidas foi avaliado pela peroxidação lipídica e pelas actividades da catalase (CAT), ascorbato peroxidase (APX), guaiacol peroxidase (GPX) e superóxido dismutase (SOO), quer na raiz quer na parte aérea. Foi observado um aumento significativo (versus controlo) na peroxidação lipídica e actividade enzimática da CATe APX na parte aérea da B. juncea, N. tabacum e S. nigrum para os níveis de contaminação mais elevados, 15 e/ou 35 mg Cd kg-1 A B. juncea apresentou maior sensibilidade na resposta da GPX, para todas as concentrações de Cd no solo. A peroxidação lipídica e a actividade da CAT foram superiores na parte aérea em relação à raiz para todas as plantas em todas as contaminações de Cd presentes no solo. A actividade da SOO não apresentou respostas consistentes para nenhuma das plantas. ABSTRACT: Remediation of sites contaminated with heavy metals using hyper accumulators seems a promising alternative to engineering approaches. ln this work, we compared cadmium (Cd) accumulation and tolerance (based on responses to oxidative stress) in three different species, Brassica juncea (L) Czem., Nicotiana tabacum L. and Solanum nigrum L., described in the literature as very tolerant or even as hyper accumulators. The plants were grown in soil spiked with different Cd concentrations (O- 35 mg kg- 1) over a period of 90 days. The translocation factor (TF), used to measure the effectiveness of translocating Cd from roots to shoots, depended greatly on the species. N. tabacum was the plant which exhibited the highest TF values. lt was the only plant under study that fulfilled the conditions of a hyper accumulator for all levels of soil contamination. On the other hand, S. nigrum presented the highest Cd concentration in plant tissues, with TF > 1 in the presence of 5 mg Cd kg-1 of soil. Although B. juncea had presented the lowest TF and Cd concentrations, it was the only plant with TF values increasing with the level of cadmium. Oxidative stress in plants was evaluated by lipid peroxidation and activities of catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and superoxide dismutase (SOO), both in roots and shoots. A significant enhancement (versus control) on lipid peroxidation and enzymatic activity of CAT and APX in shoots of B. juncea, N. tabacum and S. nigrum was observed for the highest levels of Cd in soil, 15 and/or 35 mg Cd kg-1. B. juncea presented the most sensitive response of GPX, for all levels of Cd in soil. Lipid peroxidation and CAT activity were greater in shoots than in roots for all plants and soil Cd concentrations. SOO activity did not present consistent trends for any plant.

Nanostructured Systems for Electrocatalysis of Reduction Reactions for Energy Conversion Applications

Oxygen Reduction Reaction (ORR) requires a platinum-based catalyst to reduce the activation barrier. One of the most promising materials as alternative catalysts are carbon-based, graphene and carbon nanotubes (CNT) derivatives. ORR on a carbon-based substrate involves the less efficient two electrons process and the optimal four electrons process. New synthetic strategies to produce tunable graphene-based materials utilizing graphene oxide (GO) as a base inspired the first part of this work. Hydrogen Evolution Reaction (HER) is a slow process requiring also platinum or palladium as catalyst. In the second part of this work, we develop and use a technique for Ni nanoparticles electrodeposition using NiCl2 as precursor in the presence of ascorbate ligands. Electrodeposition of nano-nickel onto flat glassy carbon (GC) and onto nitrogen-doped reduced graphene oxide (rGO-N) substrates are studied. State of the art catalysts for CO2RR requires rare metals rhenium or rhodium. In recent years significant research has been done on non-noble metals and molecular systems to use as electro and photo-catalysts (artificial photosynthesis). As Cu-Zn alloys show good CO2RR performance, here we applied the same nanoparticle electrosynthesis technique using as precursors CuCl2 and Cl2Zn and observed successful formation of the nanoparticles and a notable activity in presence of CO2. Using rhenium complexes as catalysts is another popular approach and di-nuclear complexes have a positive cooperative effect. More recently a growing family of pre-catalysts based on the earth-abundant metal manganese, has emerged as a promising, cheaper alternative. Here we study the cooperative effects of di-nuclear manganese complexes derivatives when used as homogeneous electrocatalysts, as well as a rhenium functionalized polymer used as heterogeneous electrocatalyst.