Douglas Carvalho Amaral

Bioaccumulation and effects of lanthanum on growth and mitotic index in soybean plants.

Rare earth elements such as lanthanum (La) have been used as agricultural inputs in some countries in order to enhance yield and improve crop quality. However, little is known about the effect of La on the growth and structure of soybean, which is an important food and feed crop worldwide. In this study, bioaccumulation of La and its effects on the growth and mitotic index of soybean was evaluated. Soybean plants were exposed to increasing concentrations of La (0, 5, 10, 20, 40, 80, and 160 µM) in nutrient solution for 28 days. Plant response to La was evaluated in terms of plant growth, nutritional characteristics, photosynthetic rate, chlorophyll content, mitotic index, modifications in the ultrastructure of roots and leaves, and La mapping in root and shoot tissues. The results showed that the roots of soybean plants can accumulate sixty-fold more La than shoots. La deposition occurred mainly in cell walls and in crystals dispersed in the root cortex and in the mesophyll. When La was applied, it resulted in increased contents of some essential nutrients (i.e., Ca, P, K, and Mn), while Cu and Fe levels decreased. Moreover, low La concentrations stimulated the photosynthetic rate and total chlorophyll content and lead to a higher incidence of binucleate cells, resulting in a slight increase in roots and shoot biomass. At higher La levels, soybean growth was reduced. This was caused by ultrastructural modifications in the cell wall, thylakoids and chloroplasts, and the appearance of c-metaphases.

Paragênese mineral de solos desenvolvidos de diferentes litologias na região sul de Minas Gerais

Estudos sistematicos sobre os fatores de formacao do solo sao relativamente escassos no Brasil, em razao da dificuldade de amostrar varios niveis de um fator, mantendo os demais constantes. A regiao de Lavras, MG, possui grande diversidade geologica em uma area pequena, o que possibilita avaliar o controle exercido por diferentes litologias na mineralogia e nas demais caracteristicas do solo. Foram selecionados oito solos embasados sobre quartzito, mica-xisto, gabro, itabirito, serpentinito, metacalcario, gnaisse e filito, em condicoes semelhantes de vegetacao (floresta tropical semidecidual), relevo (terco medio de encosta) e clima. Apos a descricao dos perfis, coletaram-se amostras dos horizontes e das rochas, e realizaram-se analises fisicas e quimicas de rotina, composicao quimica total e mineralogia da rocha, da areia e da argila do solo. Todos os solos sao pobres em bases trocaveis (exceto o Argissolo sobre itabirito), e notou-se grande variacao na composicao granulometrica, mineralogica e quimica. Os teores de Al2O3, SiO2 e Fe2O3 presentes nas rochas nao evidenciaram correlacao com os respectivos teores nos solos derivados, enquanto o teor de Fe2O3 foi fortemente correlacionado a densidade de particulas e suscetibilidade magnetica. Apesar de evidencias de material parcialmente aloctone em alguns casos, pode-se notar forte influencia da litologia subjacente na paragenese mineralogica. Os solos foram genericamente agrupados em: cauliniticos com minerais 2:1 (Argissolos sobre mica-xisto e itabirito; e Cambissolo sobre quartzito), cauliniticos (Argissolos sobre gnaisse e filito) e oxidicos (Latossolos sobre metacalcario e gabro; e Plintossolo sobre serpentinito). Os processos de monossialitizacao e alitizacao predominam na regiao, sendo respectivamente associados a rochas com valores intermediarios e baixos em silica, enquanto a presenca de minerais 2:1 e acessoria a caulinita e parece depender da presenca de mica e altos teores de silica na rocha de origem.

A New Approach to Sampling Intact Fe Plaque Reveals Si-Induced Changes in Fe Mineral Composition and Shoot As in Rice

The Fe (oxyhydr)oxide rind, or Fe plaque, that forms on aquatic plant roots is an important sorbent of metal(loid)s and plays a role in the attenuation of metal(loid) uptake into higher plants. However, the mineral composition of Fe plaque and thus its potential to sorb metal(loid)s is affected by solution chemistry. The predominant strategy to characterize Fe plaque using dithionite-citrate-bicarbonate (DCB) extraction and elemental analysis reveals total Fe quantity but misses the mineral structure of the Fe (oxyhydr)oxide. Here, we developed a new technique using gentle sonication to sample intact Fe plaque from the root system and concentrate it for subsequent mineralogical characterization using synchrotron-based X-ray diffraction and X-ray absorption spectroscopy. We then coupled that data with conventional DCB extraction. The sample preparation method was effective at concentrating As-bound Fe plaque minerals in a uniform coating onto membranes that could easily be analyzed with X-ray techniques. Using these methods, we show that the percentage of poorly ordered Fe minerals in Fe plaque increases with increasing pore-water Si in flooded rice paddy soils. These findings have implications for understanding mineral controls on As cycling in the soil-rice nexus, and the sampling approach can be adopted for other aquatic plant systems.

Gomphrena claussenii, the first South-American metallophyte species with indicator-like Zn and Cd accumulation and extreme metal tolerance.

Plant species with the capacity to tolerate heavy metals are potentially useful for phytoremediation since they have adapted to survive and reproduce under toxic conditions and to accumulate high metal concentrations. Gomphrena claussenii Moq., a South-American species belonging to the Amaranthaceae, is found at a zinc (Zn) mining area in the state of Minas Gerais, Brazil. Through soil and hydroponic experiments, the metal tolerance and accumulation capacities of G. claussenii were assessed and the effects on physiological characteristics were compared with a closely related non-tolerant species, G. elegans Mart. G. claussenii plants grown in soil sampled at the Zn smelting area accumulated up to 5318μgg-1 of Zn and 287 μg g-1 of cadmium (Cd) in shoot dry biomass after 30 days of exposure. Plants were grown in hydroponics containing up to 3000 μM of Zn and 100 μM of Cd for G. claussenii and 100 μM of Zn and 5 μM of Cd for G. elegans. G. claussenii proved to be an extremely tolerant species to both Zn and Cd, showing only slight metal toxicity symptoms at the highest treatment levels, without significant decrease in biomass and no effects on root growth, whereas the non-tolerant species G. elegans showed significant toxicity effects at the highest exposure levels. Both species accumulated more Zn and Cd in roots than in shoots. In G. elegans, over 90% of the Cd remained in the roots, but G. claussenii showed a root:shoot concentration ratio of around 2, with shoots reaching 0.93% Zn and 0.13% Cd on dry matter base. In G. claussenii shoots, the concentrations of other minerals, such as iron (Fe) and manganese (Mn), were only affected by the highest Zn treatment while in G. elegans the Fe and Mn concentrations in shoots decreased drastically at both Zn and Cd treatments. Taking together, these results indicate that G. claussenii is a novel metallophyte, extremely tolerant of high Zn and Cd exposure and an interesting species for further phytoremediation studies.

Thymus vulgaris essential oil and thymol against Alternaria alternata (Fr.) Keissler: effects on growth, viability, early infection and cellular mode of action

BACKGROUND In initial assays, Thymus vulgaris essential oil (TEO) has demonstrated activity against several plant-pathogenic fungi and has reduced the fungal diseases to levels comparable with commercial fungicides. Thus, the goal of this work was to identify the mode of action in fungi of TEO and its major compound thymol (TOH) at the cellular level using an ultrastructure approach. RESULTS TEO from leaves and TOH had minimum inhibitory concentrations (MICs) of 500 and 250 µg mL(-1) respectively against A. alternata; under the same conditions, MIC for a commercial fungicide was 1250 µg mL(-1) . Ultrastructure analysis showed that TOH phenolic substance prevented fungal growth, reduced fungal viability and prevented the penetration in fruits by a cell wall/plasma membrane interference mode of action with organelles targeted for destruction in the cytoplasm. Such mode of action differs from protective and preventive-curative commercial fungicides used as pattern control. CONCLUSION These findings suggest that TOH was responsible for the antifungal activity of TEO. Therefore, both the essential oil and its major substance have potential for use in the development of new phenolic structures and analogues to control Alternaria brown spot disease caused by Alternaria alternata.

Essential oils on the control of stem and ear rot in maize

Stem and ear rot caused by Stenocarpella maydis are responsible for severe losses in maize production. Treatment of seeds with fungicides may induce environmental damage. Hence, this study aimed to evaluate the effects of essential oils extracted from Cymbopogon winterianus, Thymus vulgaris, Cymbopogon citratus, Corymbia citriodora, Cinnamomum zeylanicum, and Syzygium aromaticum on the development of in vitro S. maydis. In addition, maize seeds were treated with these essential oils to determine their possible mode of action and effects. The oils from S. aromaticum, C. zeylanicum, and T. vulgaris inhibited fungal development at concentrations higher than 0.025%. The oils from S. aromaticum and C. zeylanicum showed seed germination rates of 89.0% and 84.5%, which were higher than that of the control. The oils from S. aromaticum and C. zeylanicum reduced the pathogen incidence in the seeds to 39.0% and 28.0%, respectively. Further, these oils as well as that from T. vulgaris produced lower reduction of maize stand. Scanning electron microscopy examination revealed that essential oils from S. aromaticum and T. vulgaris acted directly on the conidia, impeding germination. The findings suggest that the oils from S. aromaticum, C. zeylanicum, and T. vulgaris are potential alternatives for maize seed treatment in the control of S. maydis.

ALTERAÇÕES ANATÔMICAS EM ESPÉCIE DE GRAMÍNEA CULTIVADA EM SOLO DE ÁREA DE MINERAÇÃO DE ZINCO TRATADO COM MATERIAIS AMENIZANTES

Concentracoes elevadas de elementos-traco em solos podem representar riscos ao ambiente e aos humanos. Diante disso, diversas tecnologias tem sido utilizadas para mitigar estes riscos, sendo a fitorremediacao uma tecnica de baixo custo e ambientalmente correta. Plantas expostas a altas concentracoes de elementos-traco podem vir a apresentar alteracoes anatomicas e ultraestruturais em resposta a fitotoxidez. Materiais amenizantes podem minimizar essas alteracoes, visto que alem de reduzirem a fitodisponibilidade destes elementos, tambem podem melhorar as condicoes do solo. Neste contexto, estudos que utilizam a Microscopia Eletronica para avaliacao destas alteracoes ocorridas em plantas tornam-se de grande valia na avaliacao de possiveis efeitos de estresse para as estruturas celulares internas, bem como para entender possiveis mecanismos de tolerância das especies. A Microscopia Eletronica de Varredura (MEV) tem evoluido na direcao de dar nao apenas informacoes ultraestruturais, mas tambem analiticas das amostras estudadas. Contando ainda com um detector de dispersao de Raios-X, pode-se, atraves da tecnica da Espectroscopia de Energia Dispersiva (EDS), alem de gerar imagens, determinar a composicao quimica do especime em estudo. Objetivou-se com este trabalho evidenciar, por meio de analises qualitativas e quantitativas usando MEV/EDS, possiveis alteracoes anatomicas e ultraestruturais em Andropogon sp. cultivado em solos de areas de mineracao de zinco tratados com materiais amenizantes. O experimento foi conduzido em casa de vegetacao, utilizando-se tres solos, dois materiais amenizantes, 2 doses de cada material amenizante e tres repeticoes. Os amenizantes foram incubados por 60 dias e, apos esse periodo, realizou-se a semeadura de 15 sementes de Andropogon sp., autoctone de uma area de mineracao de zinco localizada em Vazante (MG). Apos o cultivo, amostras de folhas e raizes foram analisadas por MEV/EDS. As plantas apresentaram folhas com desestruturacao do mesofilo, deformacao em celulas epidermicas e em celulas da bainha dos feixes vasculares. As raizes apresentaram as celulas epidermicas, do cortex e da medula deformadas e rompidas, alem de vasos do cilindro vascular rompidos. Foram localizadas, tambem, em celulas epidermicas, feixes vasculares, cortex e medula estruturas diferenciadas e, ou, cristais que continham teores significativos de Zn e Pb. O residuo de carvao foi eficiente como amenizante da fitotoxidez causada por ETs como Zn, Cd e Pb, reduzindo o estresse e, consequentemente, as alteracoes anatomicas nas plantas. Por outro lado, o lodo de esgoto nao apresentou a mesma eficiencia. Andropogon sp. foi capaz de sobreviver as alteracoes atraves de mecanismos de acumulo de Zn e Pb em estruturas e, ou cristais.