Fábio Lopes Olivares

Humic Acids Isolated from Earthworm Compost Enhance Root Elongation, Lateral Root Emergence, and Plasma Membrane H+-ATPase Activity in Maize Roots

Earthworms (Eisenia foetida) produce humic substances that can influence plant growth by mechanisms that are not yet clear. In this work, we investigated the effects of humic acids (HAs) isolated from cattle manure earthworm compost on the earliest stages of lateral root development and on the plasma membrane H+-ATPase activity. These HAs enhance the root growth of maize (Zea mays) seedlings in conjunction with a marked proliferation of sites of lateral root emergence. They also stimulate the plasma membrane H+-ATPase activity, apparently associated with an ability to promote expression of this enzyme. In addition, structural analysis reveals the presence of exchangeable auxin groups in the macrostructure of the earthworm compost HA. These results may shed light on the hormonal activity that has been postulated for these humic substances.

Bioactivity of chemically transformed humic matter from vermicompost on plant root growth.

Chemical reactions (hydrolysis, oxidation, reduction, methylation, alkyl compounds detachment) were applied to modify the structure of humic substances (HS) isolated from vermicompost. Structural and conformational changes of these humic derivatives were assessed by elemental analyses, size exclusion chromatography (HPSEC), solid-state nuclear magnetic resonance ((13)C CPMAS-NMR), and diffusion ordered spectroscopy (DOSY-NMR), whereas their bioactivity was evaluated by changes in root architecture and proton pump activation of tomato and maize. All humic derivatives exhibited a large bioactivity compared to original HS, both KMnO(4)-oxidized and methylated materials being the most effective. Whereas no general relationship was found between bioactivity and humic molecular sizes, the hydrophobicity index was significantly related with proton pump stimulation. It is suggested that the hydrophobic domain can preserve bioactive molecules such as auxins in the humic matter. In contact with root-exuded organic acids the hydrophobic weak forces could be disrupted, releasing bioactive compounds from humic aggregates. These findings were further supported by the fact that HS and all derivatives used in this study activated the auxin synthetic reporter DR5::GUS.

Bioatividade de ácidos húmicos: efeitos sobre o desenvolvimento radicular e sobre a bomba de prótons da membrana plasmática

The bioactivity of humic acids (HA) isolated from sludge of the station of sewer treatment (HAL) and from vermicompost (HAV) was evaluated through the action of those substances on primary transport of protons of the plasma membrane of coffee and corn root cells and its relationship with the development of those species. Axa0stimulation in the superficial area of roots was observed for both species cultivated with both humic acids, exhibiting an optimum concentration, about 40xa0mgxa0L-1 of HA. In this condition the treatment with HAL and HAV stimulated the plasma membrane H+-ATPase of corn and coffee roots. HAL were more effective to promote those effects than HAV. The modification of the chromatographic profile of the HA in solution before and after the cultivation of the seedlings revealed that the interaction plant-HA promoted a rearrangement of the average molecular weight of those substances suggesting a dynamic mobilization of bioactive subunits of the HA by plant exudates. The structural analysis of the HA has detected the presence of auxin groups. A comparative analysis of the action of those HA on the monocotyledonous (corn) and dicotyledonous (coffee) plants indicates to the activation of plasmallema H+-ATPase as a possible metabolic marker for bioactivity of humic acids.

Recobrimento de sementes de milho com ácidos húmicos e bactérias diazotróficas endofíticas

O objetivo deste trabalho foi avaliar o efeito do recobrimento de sementes de milho com acidos humicos (AH), bacterias diazotroficas endofiticas e o uso em conjunto de AH e bacterias diazotroficas endofiticas, na estimulacao do crescimento vegetal e na populacao de bacterias estabelecidas na planta hospedeira. A adicao de AH, bacterias e o uso em conjunto estimularam o crescimento vegetal. Os AH utilizados no recobrimento de sementes de milho tem menor capacidade de estimular o crescimento radicular, em comparacao ao uso em solucao. O recobrimento de sementes e uma opcao de inoculacao de bacterias diazotroficas endofiticas da especie Herbaspirillum seropedicae (Z67).

Arbuscular mycorrhizal fungi induce differential activation of the plasma membrane and vacuolar H+ pumps in maize roots

Roots undergo multiple changes as a consequence of arbuscular mycorrhizal (AM) interactions. One of the major alterations expected is the induction of membrane transport systems, including proton pumps. In this work, we investigated the changes in the activities of vacuolar and plasma membrane (PM) H+ pumps from maize roots (Zea mays L.) in response to colonization by two species of AM fungi, Gigaspora margarita and Glomus clarum. Both the vacuolar and PM H+-ATPase activities were inhibited, while a concomitant strong stimulation of the vacuolar H+-PPase was found in the early stages of root colonization by G. clarum (30xa0days after inoculation), localized in the younger root regions. In contrast, roots colonized by G. margarita exhibited only stimulation of these enzymatic activities, suggesting a species-specific phenomenon. However, when the root surface H+ effluxes were recorded using a noninvasive vibrating probe technique, a striking activation of the PM H+-ATPases was revealed specifically in the elongation zone of roots colonized with G. clarum. The data provide evidences for a coordinated regulation of the H+ pumps, which depicts a mechanism underlying an activation of the root H+-PPase activity as an adaptative response to the energetic changes faced by the host root during the early stages of the AM interaction.

Crescimento de mudas de maracujazeiro-doce inoculadas com fungos micorrízicos arbusculares e bactérias diazotróficas sob diferentes doses de fósforo

An experiment, at greenhouse conditions, was carried out to evaluate the effects of inoculation with mycorrhizal fungi (AMF) and diazotrophic bacteria, on sweet passion fruit seedling growth under different phosphorus levels. The experiment design was randomized blocks in 3x2x4 factorial, with three treatments with fungi: Gigaspora margarita, Glomus clarum and control (without fungus); two treatments with bacteria: Burkholderia sp. + Burkholderia silvatlantica and control (without bacteria); and four P levels: 0, 15, 30 and 60 mg dm-3 of soil, with four replications. The experimental unit consisted of a 3.5 dm3 pot with three plants. The seedlings were grown from seed and transplanted to pots containing a sterile soil: sand mixture (1:2 v: v). At 90 days after transplantation were assessed: height, diameter of stem, leaf area, shoot dry weight, percentage of root colonization by fungi and enumeration of diazotrophs in roots. Despite the presence of diazotrophic bacteria, inoculation with AMF provided increase in height, shoot dry weight, leaf area and stem diameter of seedlings, both at 0 and 15 mg dm-3 of P levels. Bacteria increased height and leaf area in shoots when associated with the AMF species of G. margarita, however in the absence of AMF, they reduced the shoot dry mass, regardless of P levels in the substrate.

Fungos micorrízicos arbusculares, bactérias diazotróficas e adubação fosfatada em mudas de mamoeiro

Conduziu-se um experimento em casa de vegetacao para avaliar o crescimento de mudas de mamoeiro inoculadas com fungos micorrizicos arbusculares (FMAs) e com bacterias diazotroficas, na ausencia e presenca de fosforo. O delineamento experimental foi o de blocos casualizados, em arranjo fatorial 4 x 3 x 2, sendo os tratamentos compostos por: especies de fungos micorrizicos arbusculares Glomus clarum, Gigaspora margarita, o inoculo misto Glomus clarum + Gigaspora margarita e o controle sem FMAs; as bacterias diazotroficas Stenotrophomonas maltophilia e Azospirillum sp. e o controle sem bacteria diazotrofica; duas doses de fosforo no solo, 0 e 25 mg dm-3, todos com quatro repeticoes. Aos 105 dias apos a semeadura, as plantas foram coletadas e avaliadas quanto a altura, area foliar total, diâmetro do caule, materia seca da parte aerea, da raiz e materia seca total, porcentagem de colonizacao micorrizica e contagem de bacterias diazotroficas nas raizes. As inoculacoes com os FMAs proporcionam aumentos significativos no crescimento das mudas de mamoeiro, mesmo em condicoes de baixa disponibilidade de fosforo, independentemente da presenca de bacteria diazotrofica. O fungo G. margarita e o inoculo misto G. margarita + G. clarum destacam-se como os mais promissores para a cultura do mamoeiro. A inoculacao com bacterias diazotroficas, na ausencia ou na presenca de FMAs, nao propiciou efeito estimulatorio ou supressivo no crescimento das mudas de mamoeiro.