Elisa Monteze Bicalho

Control of macaw palm seed germination by the gibberellin/abscisic acid balance

The hormonal mechanisms involved in palm seed germination are not fully understood. To better understand how germination is regulated in Arecaceae, we used macaw palm (Acrocomia aculeata (Jacq.) Lodd. Ex Mart.) seed as a model. Endogenous hormone concentrations, tocopherol and tocotrienol and lipid peroxidation during germination were studied separately in the embryo and endosperm. Evaluations were performed in dry (D), imbibed (I), germinated (G) and non-germinated (NG) seeds treated (+GA3 ) or not treated (control) with gibberellins (GA). With GA3 treatment, seeds germinated faster and to a higher percentage than control seeds. The +GA3 treatment increased total bioactive GA in the embryo during germination relative to the control. Abscisic acid (ABA) concentrations decreased gradually from D to G in both tissues. Embryos of G seeds had a lower ABA content than NG seeds in both treatments. The GA/ABA ratio in the embryo was significantly higher in G than NG seeds. The +GA3 treatment did not significantly affect the GA/ABA ratio in either treatment. Cytokinin content increased from dry to germinated seeds. Jasmonic acid (JA) increased and 1-aminocyclopropane-1-carboylic acid (ACC) decreased after imbibition. In addition, α-tocopherol and α-tocotrienol decreased, while lipid peroxidation increased in the embryo during germination. We conclude that germination in macaw palm seed involves reductions in ABA content and, consequently, increased GA/ABA in the embryo. Furthermore, the imbibition process generates oxidative stress (as observed by changes in vitamin E and MDA).

Ciprofloxacin induces oxidative stress in duckweed (Lemna minor L.): Implications for energy metabolism and antibiotic-uptake ability

We investigate the physiological responses and antibiotic-uptake capacity of Lemna minor exposed to ciprofloxacin. Ciprofloxacin (Cipro) induced toxic effects and hormesis in plants by significantly modifying photosynthesis and respiration pathways. A toxic effect was induced by a concentration ≥1.05mg ciprofloxacin l-1 while hormesis occurs at the lowest concentration studied (0.75mg ciprofloxacin l-1). By impairing normal electron flow in the respiratory electron transport chain, ciprofloxacin induces hydrogen peroxide (H2O2) production. The ability of plants to cope with H2O2 accumulation using antioxidant systems resulted in stimulation/deleterious effects to photosynthesis by Cipro. Cipro-induced oxidative stress was also associated with the ability of L. minor plants to uptake the antibiotic and, therefore, with plant-uptake capacity. Our results indicate that instead of being a photosystem II binding molecule, Cipro induces oxidative stress by targeting the mitochondrial ETC, which would explain the observed effects of the antibiotic on non-target eukaryotic organisms. The selection of plants species with a high capacity to tolerate oxidative stress may constitute a strategy to be used in Cipro-remediation programs.

Alterations in seed reserves of Dalbergia nigra ((Vell.) Fr All. ex Benth.) during hydration

Seed imbibitions is the first stage of the germination process and is characterized by the hydration of tissues and cells and the activation and/or induction of the enzymes responsible for mobilizing reserves for respiration and the construction of new cell structures. The objective of this study was to investigate the alterations in reserve substances during slow hydration of Bahia Rosewood (Dalbergia nigra) seeds in water. Seeds from two different lots (Lot I and II) were placed in saturated desiccators (95-99% RH) to hydrate at 15 and 25 °C until water contents of 10, 15, 20 and 25% were reached. At each level of hydration, changes in lipid reserves, soluble carbohydrates, starch and soluble proteins were evaluated. The mobilization of reserves was similarly assessed in both lots, with no differences being observed between the two hydration temperatures. Lipid contents showed little variation during hydration, while the contents of soluble carbohydrates and starch decreased after the 15% water content level. Soluble proteins showed a gradual tendency to decrease between the control (dry seeds) up to 25% water content.

Integrative effects of zinc and temperature on germination in Dimorphandra wilsonii rizz.: Implications of climate changes

The integrative effects of zinc (Zn; 0 mg L-1 , 75 mg L-1 , 150 mg L-1 , and 200 mg L-1 ) and temperature (25 °C, 30 °C, and 35 °C) on seed germination of the threatened Brazilian species Dimorphandra wilsonii were evaluated. Zinc effects on seed germination were only observed at 30 °C and 35 °C. By stimulating respiration rates, rising temperatures accentuate hydrogen peroxide (H2 O2 ) formation in germinating seeds in the presence of Zn. Seed Zn tolerance was related to the activation of enzymatic antioxidants, and ascorbate peroxidase (APX) activity had a central role in H2 O2 scavenging under the highest temperatures tested. Increased APX activity allowed successful germination, whereas decreasing APX activity was accompanied by decreasing germination rates in Zn-treated seeds at 35 °C. Within a scenario of future climate change, it will be extremely important to avoid increasing Zn concentrations in natural habitats that would threaten conservation efforts directed toward this endangered plant species. Environ Toxicol Chem 2017;36:2036-2042.

Long-term persistence of Velloziaceae species in the soil seed bank in campo rupestre vegetation, Brazil

Background: Soil seed banks play an important role in regeneration in many ecosystems and contribute to ecosystem resilience in disturbed environments. This is especially true for the Brazilian campo rupestre, a fire-prone ecosystem that harbours a large number of endangered endemic species. Aims: We aimed to determine the persistence in the soil seed bank, through the evaluation of the in situ longevity, of seeds from four species of Velloziaceae, an endemic-rich and dominant family in the campo rupestre vegetation. Methods: Seeds of four sympatric and common Vellozia species were collected and placed in bags, which were buried in their natural area of occurrence. The germination capacity of the buried seeds was regularly evaluated under controlled light and temperature conditions over a 5-year period. Results: No in situ establishment was observed for any of the buried seeds. All species retained high germinability throughout the burial, except for V. glandulifera, whose germinability was reduced by 60%. The reduction in germinability of V. glandulifera was positively correlated with seed size and mass. Conclusions: Seeds of the studied species of Vellozia are capable of persisting in soil over time while maintaining high germinability. Seed traits appear to be important for seed bank persistence.

Glyphosate Can Decrease Germination of Glyphosate-Resistant Soybeans

We investigated the effects of different concentrations of glyphosate acid and one of its formulations (Roundup) on seed germination of two glyphosate-resistant (GR) and one non-GR variety of soybean. As expected, the herbicide affected the shikimate pathway in non-GR seeds but not in GR seeds. We observed that glyphosate can disturb the mitochondrial electron transport chain, leading to H2O2 accumulation in soybean seeds, which was, in turn, related to lower seed germination. In addition, GR seeds showed increased activity of antioxidant systems when compared to non-GR seeds, making them less vulnerable to oxidative stress induced by glyphosate. The differences in the responses of GR varieties to glyphosate exposure corresponded to their differences in enzymatic activity related to H2O2 scavenging and mitochondrial complex III (the proposed site of ROS induction by glyphosate). Our results showed that glyphosate ought to be used carefully as a pre-emergence herbicide in soybean field crop systems because this practice may reduce seed germination.

Atividades de α-galactosidase e poligalacturonase durante a hidratação de sementes de Dalbergia nigra ((Vell.) Fr. All. ex Benth.) sob diferentes temperaturas

Germination is a process that begins with seed water uptake, stimulating enzyme synthesis or activating enzymes already present. The objective of this study was to evaluate variations in monosaccharide reserves and the activities of the α-galactosidase and polygalacturonase enzymes during the hydration of two lots of Dalbergia nigra (Bahia Rosewood) seeds. Seeds from different origins constituted the two lots I and II, classified as high and low vigor, respectively. Both lots were placed in desiccators with a high relative humidity to hydrate and at 15 and 25 °C until levels of 10, 15, 20 and 25% moisture levels in seeds were reached. The seed cotyledons were analyzed for the quantity of monosaccharides and enzyme activity. The control had higher concentrations of xylose and rhamnose, which decreased during hydration until the 15% level was reached, after which concentrations increased again in both lots. Lot I, with a superior quality, showed higher glucose synthesis and degradation during seed hydration. Both enzymes were pre-existing since activity was already present in the seeds without imbibition. The polygalacturonase enzyme increased and the α-galactosidase enzyme remained relatively constant during seed hydration.

Effects of Ciprofloxacin and Roundup on seed germination and root development of maize

Their continuous release into the environment, associated with their inherent biological activity, has motivated investigations into the detrimental effects of antibiotics and herbicides in natural and agricultural ecosystems. In this study, the interactive effects of the antibiotic ciprofloxacin (Cipro) and the herbicide Roundup on seed germination and root development were investigated. Although both compounds act as inhibitors of the mitochondrial electron transport chain in seeds, neither Cipro nor Roundup disrupted germinability of maize seeds. However, Cipro accelerated germination by promoting ROS accumulation in seeds, while the stimulatory effect of Roundup on ROS-scavenging enzymes (catalase and ascorbate peroxidase) seems to prevent ROS-signaling, delaying the germination process. Roundup reduced root elongation, possibly due to its interference with auxin production, thereby preventing cell division, while Cipro stimulated root elongation by increasing root oxidative status. Cipro and Roundup showed antagonistic effects on maize seeds and root physiology. The presence of the antibiotic is likely not to disturb plant development; however, its stimulatory effects were not sufficient to overcome the deleterious effects of Roundup. According to our results, glyphosate-based herbicides must be carefully used during maize cropping and although antibiotics such as Cipro may not negatively impact agricultural production, their accumulation by crops must be investigated since this can be a pathway of antibiotic-insertion into the food chain.

Ciprofloxacin vs. temperature: Antibiotic toxicity in the free-floating liverwort Ricciocarpus natans from a climate change perspective

The physiological responses of the aquatic liverwort Ricciocarpus natans to ciprofloxacin (Cipro) exposure under different growth temperatures were investigated. Cipro appears to act as an inhibitor of mitochondrial Complex III by blocking the oxidation of quinol, resulting in the formation of hydrogen peroxide (H2O2). H2O2 accumulation upon Cipro exposure is responsible for decreased photosynthesis in plants. The amount of H2O2 in plants is kept under control by antioxidant enzymes, whose activities are central to the responses of plants to Cipro yet are influenced by temperature. Increased temperature favored Cipro uptake by plants as well as its deleterious effects on mitochondrial activity; however, it also favored the activity of antioxidant enzymes, thereby preventing the exacerbation of the deleterious effects of Cipro. The uptake of Cipro by plants appears to be largely a passive process, although some uptake must be driven by an energy-consuming process. Ricciocarpus natans should be considered for programs aimed at the reclamation of Cipro since this plant exhibits high Cipro-tolerance, the capacity for accumulation and increased uptake rates of the antibiotic with increasing temperatures (from 20 to 30 °C).

SUPERAÇÃO DA DORMÊNCIA DAS SEMENTES DE Delonix regia (Bojer ex Hook.) Raf.

RESUMO – Delonix regia (flamboyant) e uma especie arborea amplamente utilizada no Brasil, de alto valor ornamental. Sua propagacao ocorre por meio de sementes, que apresentam dormencia pela impermeabilidade do tegumento a agua. Com o objetivo de determinar a melhor metodologia para a superacao da dormencia, as sementes da especie foram submetidas a diferentes tratamentos: 1) imersao em agua fervente por 1 min; 2) imersao em agua a 80 °C e a 90 °C por 1 e 3 min; 3) escarificacao manual com lixa; e 4) imersao em acido sulfurico concentrado por 15, 30, 45 e 60 min, alem da testemunha. Apos cada tratamento, as sementes foram colocadas para germinar em rolo de papel, na temperatura de 25 oC. Em uma segunda etapa, os tratamentos mais efetivos na quebra de dormencia das sementes foram aplicados e a germinacao, testada a temperatura de 30 °C. Em ambas as temperaturas, as contagens de germinacao (plântulas normais) foram realizadas diariamente. O tratamento das sementes de flamboyant em agua quente a 90 oC por 1 min foi o mais eficiente na promocao da germinacao, sendo pratico e dispensando o uso de tratamentos quimicos. O teste de germinacao realizado a temperatura de 30 °C nao forneceu resultados satisfatorios, com menores porcentagens de plântulas normais e IVG que os testes a 25 oC. Foram descritas como plântulas normais as que possuiam visiveis dois cotiledones semiabertos, hipocotilo alongado, raiz primaria bem desenvolvida e raizes adventicias curtas. Conclui-se que sementes de Delonix regia germinam melhor a 25 oC apos a imersao por 1 min em agua a 90 oC, sendo este indicado como tratamento para superacao da dormencia da especie. Palavras-chave: Flamboyant; Germinacao; Temperatura. OVERCOMING SEED DORMANCY OF Delonix regia (Bojer ex Hook.) Raf.