Efeito da pressurização com CO2 sobre o pH da água

Durante a fase de desenvolvimento de novos produtos fitossanitários é comumente utilizado o pulverizador a pressão constante, pressurizado com CO2. O gás carbônico pode provocar a acidificação da água e afetar o comportamento do composto que está sendo avaliado. No presente trabalho, amostras de água de 30 diferentes fontes foram pressurizadas com CO2 durante cinco minutos, até 275 kPa (40 lbf/pol.2), e o pH foi medido na água que saiu do bico e na água no inteior do tanque do pulverizador. Os resultados mostraram redução nos valores do pH em toda as amostras . Os valores do pH elevaram-se ligeiramente após a saída da água pelo bico do pulverizador. A redução, em alguns casos, foi marcante, atingindo 4,91 unidades de pH no caso mais drástico. Esses dados levam a recomendar cautela na interpretação dos resultados obtidos com o uso dos pulverizadores pressurizados com o gás carbônico.

Liberação de CO2, biomassa microbiana e fósforo disponível em solo adicionado de matéria seca de poaia-branca

O presente experimento, inteiramente casualizado, foi desenvolvido em condições de laboratório no Departamento de Defesa Fitossanitária, FCA/UNESP - Botucatu, entre julho e setembro de 1992. Amostras de Areia Quartzosa equivalentes à 40 g de terra seca à 105 oC ± 2 com ou sem adição de 1,9 g de matéria seca de plantas de poaia-branca (Richardia brasiliensis), 0,19 g de nitrogênio (NH4)2SO4 e 0,88 g de apatita de Araxá, foram incubadas no escuro a 25 o C ± 2 , com umidade mantida a 60% da capacidade de retenção de água. Durante a incubação, determinou-se o CO2 liberado, utilizando-se o método de retenção em NAOH seguida de titulometria com HCl; a biomassa microbiana, método de fumigação-incubação; o pH e a quantidade de fósforo extraído por resina. A maior liberação de CO2 ocorreu durante os dez primeiros dias de incubação, com 77% do total de carbono liberado nos tratamentos com adição de poaia, e 37% nos tratamentos sem adição da mesma. A liberação de CO2 foi 57 vezes maior nos tratamentos com poaia em relação ao controle. A poaia também provocou aumentos na biomassa microbiana (média de 8 vezes a biomassa do tratamento controle), e a adição de nitrogênio e/ou fosfato de rocha junto à poaia antecipou os picos de formação de biomassa de 20 para 10 dias de incubação. Os níveis de fósforo disponível foram maiores no tratamento com adição de fosfato de rocha apenas. A poaia também alcalinizou o sistema, não permitindo desta forma, observar-se relação significativa entre pH e teor de fósforo disponível.

Avaliação da decomposição de plantas aquáticas no solo através da liberação de CO2

O objetivo deste trabalho foi avaliar a decomposição de três espécies de plantas aquáticas imersas, incorporadas ao solo, provenientes do controle mecânico, em reservatórios de usinas hidrelétricas. O estudo foi realizado em casa de vegetação, localizada no Núcleo de Pesquisas Avançadas em Matologia (NUPAM) da FCA/Unesp-Botucatu. A avaliação foi conduzida em vasos contendo 14 kg de solo, com três incorporações de 50 e 100 t MF de plantas ha-1, sob duas condições de solo: seco e úmido. Com a simulação de descarte da biomassa coletada e incorporada ao solo, pôde-se conhecer, através da liberação de CO2, a degradação de três espécies de macrófitas aquáticas submersas. Para quantificação do CO2 liberado, em cada vaso foi acondicionado um frasco com solução de NaOH, sendo, logo após, lacrados e incubados por 24 horas; em seguida, foram titulados com HCl. Para ajuste e interpolação dos dados, estes foram analisados seguindo modelo de Mitscherlich, com algumas modificações. As liberações acumuladas em solo úmido foram de 1.294 e 1.582 kg CO2 ha-1, sendo 6,2 e 5,6 vezes superiores ao ocorrido em solo seco, para 50 e 100 t MF ha-1, respectivamente, observando-se que cerca de 55% da liberação de CO2 ocorreu nos primeiros 30 dias. Pode-se concluir que o solo seco é a melhor condição para descarte e incorporação da biomassa, porém deverá existir um sistema de irrigação para que o processo de degradação da biomassa incorporada seja acelerado.

Evolução de CO2 e atividades enzimáticas em amostras de solo tratado com herbicidas

Os efeitos dos herbicidas bentazon, metolachlor, trifluralin, imazethapyr, imazethapyr+lactofen, haloxyfop-methyl, glyphosate e chlorimuron-ethyl, testados em duas concentrações (duas e dez vezes a dose média recomendada por hectare), sobre a atividade microbiana foram estudados em amostras de solo que nunca haviam recebido tratamento com pesticidas. Como bioindicadores, utilizou-se a respiração microbiana, quantificando a emissão de CO2 aos 2, 4, 8, 12, 16, 20 e 24 dias após incubação, a atividade da enzima desidrogenase e a hidrólise de diacetato de fluoresceína (FDA), aos 8 e 28 dias. Bentazon e a mistura de imazethapyr+lactofen na maior concentração e o haloxyfop-methyl nas duas concentrações apresentaram efeitos inibitórios na respiração edáfica, embora diferentes em época e duração do efeito. Nenhum dos tratamentos herbicidas afetou a hidrólise da FDA. A atividade da desidrogenase foi inibida, o que foi verificado em análise realizada aos oito dias,nas amostras de solo com alta concentração de bentazon e imazethapyr; no entanto, foi estimulada nos tratamentos com baixa concentração de metolachlor e imazethapyr e na maior concentração de glyphosate. A respiração basal e a atividade da desidrogenase mostraram maior sensibilidade na detecção de efeitos dos herbicidas sobre a microbiota do solo que as determinações da hidrólise de FDA. Apenas foi encontrada correlação significativa entre a atividade da desidrogenase e a respiração basal aos oito dias de incubação. Os resultados destacam a importância da consideração de múltiplos indicadores na avaliação dos efeitos de herbicidas na microbiota do solo.

Determination of photosynthetic pigments in fleabane biotypes susceptible and resistant to the Herbicide Glyphosate

Chlorophylls and carotenoids are the main photosynthetic pigment in plants. In the weeds, the greatest amount of photosynthetic pigments can result in high competitiveness of the species. The aim of this study was to quantify the content of photosynthetic pigments in biotypes of fleabane (Conyza bonariensis) susceptible and resistant to glyphosate, by two different methods, as well as a correlation between chlorophyll content obtained by portable and classical methodology (extractable chlorophyll). An experiment was conducted in greenhouse and laboratory, 2 x 5 factorial scheme, where factor A was equivalent to biotypes of fleabane (resistant and susceptible to glyphosate) and factor B to developmental stages plants (rosette vegetative I, II and III and reproduction). At all stages of development, fleabane plants were evaluated with the portable determiner (chlorophyll content) and then the same leaves were subjected to classical methodology laboratory (extractable pigments). The resistant biotype of fleabane showed higher contents of chlorophyll a, b, and total carotenoids, inferring a greater competitive potential regarding the susceptible population to the herbicide. The portable determiner of chlorophyll showed high correlation with the classical method of determination of photosynthetic pigments, and can thus be used to accurately assess this, saving time and reagents.

Multiple forms of cotyledonary b-galactosidases from Vigna unguiculata quiescent seeds

Cotyledonary b-galactosidases were isolated and partially purified from Pitiúba cowpea (Vigna unguiculata (L.) Walp.) quiescent seeds. The purification steps consisted of precipitation of the crude extract with ammonium sulphate in the range of 20-60% saturation, acid precipitation, DEAE-Sephadex ion-exchange chromatography and Lactosyl-Sepharose affinity chromatography. This purification process gave rise to three b-galactosidases-rich fractions: b-gal I, b-gal II and b-gal III, which were purified about 5, 509, and 62 fold, respectively. They reached maximal enzyme activity at different pH ranges: 3.5-4.5 for b-gal I, 3.0-3.5 for b-gal II, and 3.0-4.0 for b-gal III. Their maximal activities were reached when the temperature of the assay medium was 60° C, and preincubation of the enzymes at different temperatures has shown that they were heat-stable up to 50° C. There were no significant differences among the partially purified enzymes as far as their response to the different effectors tested, except for Mn2+ and EDTA, which affected differently b-gal I, b-gal II, and b-gal III. They were slightly affected by Mg2+, Ca2+, Zn2+, Co2+, tartarate, molybdate, glucose, and lactose, strongly inhibited by Cu2+ and galactose, and inactivated by Hg2+. These chemical and physical properties are similar to the ones found for other plant b-galactosidases. Although through this process of purification three isoforms of this enzyme were obtained, isoelectric focusing in polyacrylamide slab gel of these enzyme-proteins suggest that cotyledons of Pitiúba cowpea quiescent seeds possess four isoforms of b-galactosidases.

Effects of iron-ore particles on propagule release, growth and photosynthetic performance of Sargassum vulgare C. Agardh (Phaeophyta, Fucales)

The effect of iron-ore particles on the propagule release and growth of Sargassum vulgare C. Agardh was tested under treatments with different concentrations of iron-ore particles: 0.1, 1.0, 10.0 g.L-1 and a solution of 10.0 g.L-1 of filtered iron-ore. Filtered seawater was used as control. Photosynthesis vs. irradiance (P-I) curves were calculated for S. vulgare in the presence of iron-ore and in seawater. There was no significant difference in the number of propagules released by the receptacles or in the percentage of zygote formation among the treatments. The released propagules acted like aggregation centers for the particles, those more heavily coated with iron (10.0 g.L-1) exhibiting the highest sinking velocity (32.6 ± 9.8 mm.s-1). No difference in the percentage of embryo survival was detected during the first week in culture. After four weeks the embryos grew in all treatments. Maximum frond development (5.3 ± 0.8 mm) was observed in treatment of seawater enriched with Provasoli's medium (PES) while initial filoids did not develop in three treatments without PES and with iron-ore (0.1 g.L-1, 1.0 g.L-1 and 10.0 g.L-1). The values for Pmax, alpha and respiration showed no significant differences between the P-I curves. The calculated value for I K was 106.26 µmol.m-2.s-1 to the control curve and 981.49 µmol.m-2.s-1 to the iron-ore curve. The results indicate that the iron-ore particles in high concentration reduce the growth of S. vulgare as they recovered the embryos, juveniles and young plants. In contrast, the presence of the particles did not affect the release of gametes, percentage of zygote formation or the percentage of embryo survival.

Synecological comparisons sustained by ecophysiological fingerprinting of intrinsic photosynthetic capacity of plants as assessed by measurements of light response curves

In some literature variations in photosynthetic rates are considered to be of little relevance for individual fitness. This depends among other things on how one defines fitness, i.e. if one takes strictly Darwinian fitness as seed production or if one needs to evaluate particular traits and consider plant establishment. It also matters if one takes the Darwinian "organism individual" as the central entity in evolution ("individual fitness") or the "species individual" in a modified "Structure of Evolutionary Theory" sensu Stephen Jay Gould. A phenotypically expressed trait like photosynthetic rate, even if intra- and interspecific differences may be small, can matter in habitat performance and niche acquisition. Light dependence curves (LCs) of photosynthetic rates are now readily measured under field conditions using miniaturized equipment of pulse amplitude modulated fluorometers. In contrast to actual momentary measurements of quantum yield of photosynthesis under actually prevailing ambient conditions, LC measurements reflect the expressed intrinsic capacity of photosynthesis. In this review we explore the power of LC measurements yielding cardinal points such as maximum apparent electron transport rate of photosystem II (ETRmax) and saturating photosynthetically active radiation (PARsat) in making intra- and interspecific comparisons of plant performance and synecological fingerprinting in ecophysiological studies across species, sites, habitats and ecosystems.

Photosynthesis and carbon gain under contrasting light levels in seedlings of a pioneer and a climax tree from a Brazilian Semideciduous Tropical Forest

In this study we evaluated photosynthetic characteristics and patterns of biomass accumulation in seedlings of two tree species from a Semideciduous Tropical Forest of Brazil. Seedlings of Trema micrantha (L.) Blum. (pioneer) and Hymenaea courbaril (L.) var. stilbocarpa (Hayne) Lee & Langenh. (climax) were grown for 4 months under low light (LL) (5%-8% of sunlight) and high light (HL) (100% of sunlight). Under HL, T. micrantha showed higher CO2 assimilation rates (A CO2) and light saturation than H. courbaril. Under LL, A CO2 were higher in H. courbaril. Under LL, total chlorophyll and carotenoid contents per unit leaf area were higher in H. courbaril. Chlorophyll a/b ratio was higher in T. micrantha under both light regimes. A CO2 and Fv/Fm ratio at both pre-dawn and midday in H. coubaril were lower in HL indicating chronic photoinhibition. Thus, the climax species was more susceptible to photoinhibition than the pioneer. However, H. courbaril produced higher total biomass under both treatments showing high efficiency in the maintenance of a positive carbon balance. Thus, both species expressed characteristics that favor growth under conditions that resemble their natural microenvironments, but H. courbaril also grew under HL. The ecophysiological range of responses to contrasting light levels of this climax plant seems to be broader than generally observed for other rainforest climax species. We propose that this could be related to the particular spatio-temporal light regime of the semideciduous forests.

A contribution to the phytogeography of Brazilian campos: an analysis based on Poaceae

Twenty areas from eight Brazilian states were compared according to a list of 224 species of Poaceae. In order to determinate affinity patterns between the areas, a binary matrix was submitted to cluster and ordination analysis. The patterns found were then faced to climate and geographic position. The scores corresponding to the areas obtained from the cluster analysis showed a strong correlation to temperature. The scores corresponding to the species suggest a gradient that associates distribution patterns to the photosynthetic pathway (C3 or C4). The current results suggest that the traditional classification of the Southern American grasslands might require some modification in order to be broadly applicable in the Brazilian context.

Photosynthetic properties of three Brazilian seaweeds

Photosynthetic performance of distinct marine macroalgae, Ulva fasciata Delile (green alga), Lobophora variegata (J. V. Lamouroux) Womersley ex E. C. Oliveira (brown alga), and Plocamium brasiliensis (Greville) M. A. Howe & W. R. Taylor (red alga), were compared using a pulse amplitude-modulated fluorometer. The maximum quantum yield (Fv/Fm) ranged from 0.80 to 0.51, and the lowest value was found in P. brasiliensis. Under 400 µmol photons m-2 s-1 irradiance, the highest value of photochemical quenching (qP = 0.92 ± 0.13) was observed for U. fasciata. The red alga P. brasiliensis dissipated high amounts of excitation energy (qN = 0.56 ± 0.09), resulting in relatively low values for the effective quantum yield of PS-II (0.23 ± 0.04), as well as for the relative electron transport rate (3.3 ± 0.7). The high photosynthetic potential found for U. fasciata partially explains the species ability for rapid growth and high productivity.

Variation in nitrogen use strategies and photosynthetic pathways among vascular epiphytes in the Brazilian Central Amazon

The variation in nitrogen use strategies and photosynthetic pathways among vascular epiphyte families was addressed in a white-sand vegetation in the Brazilian Central Amazon. Foliar nitrogen and carbon concentrations and their isotopic composition (δ15N and δ13C, respectively) were measured in epiphytes (Araceae, Bromeliaceae and Orchidaceae) and their host trees. The host tree Aldina heterophylla had higher foliar N concentration and lower C:N ratio (2.1 ± 0.06% and 23.6 ± 0.8) than its dwellers. Tree foliar δ15N differed only from that of the orchids. Comparing the epiphyte families, the aroids had the highest foliar N concentration and lowest C:N ratios (1.4 ± 0.1% and 34.9 ± 4.2, respectively). The orchids had more negative foliar δ15N values (-3.5 ± 0.2‰) than the aroids (-1.9 ± 0.7‰) and the bromeliads (-1.1 ± 0.6‰). Within each family, aroid and orchid taxa differed in relation to foliar N concentrations and C:N ratios, whereas no internal variation was detected within bromeliads. The differences in foliar δ15N observed herein seem to be related to the differential reliance on the available N sources for epiphytes, as well as to the microhabitat quality within the canopy. In relation to epiphyte foliar δ13C, the majority of epiphytes use the water-conserving CAM-pathway (δ13C values around -17‰), commonly associated with plants that live under limited and intermittent water supply. Only the aroids and one orchid taxon indicated the use of C3-pathway (δ13C values around -30‰).

Erythrocyte glucose-6-phosphate dehydrogenase activity assay and affinity for its substrate under "physiological" conditions

Glucose-6-phosphate dehydrogenase (G6PD) activity and the affinity for its substrate glucose-6-phosphate were investigated under conditions similar to the physiological environment in terms of ionic strength (I: 0.188), cation concentration, pH 7.34, and temperature (37oC). A 12.4, 10.4 and 21.4% decrease was observed in G6PD B, G6PD A+ and G6PD A- activities, respectively. A Km increase of 95.1, 94.4 and 95.4% was observed in G6PD B, G6PD A+ and G6PD A-, respectively, leading to a marked decrease in affinity. In conclusion, the observation of the reduced activity and affinity for its natural substrate reflects the actual pentose pathway rate. It also suggests a much lower NADPH generation, which is crucial mostly in G6PD-deficient individuals, whose NADPH availability is poor.

Participation of nitric oxide in the nucleus isthmi in CO2-drive to breathing in toads

The nucleus isthmi (NI) is a mesencephalic structure of the amphibian brain. It has been reported that NI plays an important role in integration of CO2 chemoreceptor information and glutamate is probably involved in this function. However, very little is known about the mechanisms involved. Recently, it has been shown that nitric oxide synthase (NOS) is expressed in the brain of the frog. Thus the gas nitric oxide (NO) may be involved in different functions in the brain of amphibians and may act as a neurotransmitter or neuromodulator. We tested the hypothesis that NO plays a role in CO2-drive to breathing, specifically in the NI comparing pulmonary ventilation, breathing frequency and tidal volume, after microinjecting 100 nmol/0.5 µl of L-NAME (a nonselective NO synthase inhibitor) into the NI of toads (Bufo paracnemis) exposed to normocapnia and hypercapnia. Control animals received microinjections of vehicle of the same volume. Under normocapnia no significant changes were observed between control and L-NAME-treated toads. Hypercapnia caused a significant (P<0.01) increase in ventilation only after intracerebral microinjection of L-NAME. Exposure to hypercapnia caused a significant increase in breathing frequency both in control and L-NAME-treated toads (P<0.01 for the control group and P<0.001 for the L-NAME group). The tidal volume of the L-NAME group tended to be higher than in the control group under hypercapnia, but the increase was not statistically significant. The data indicate that NO in the NI has an inhibitory effect only when the respiratory drive is high (hypercapnia), probably acting on tidal volume. The observations reported in the present investigation, together with other studies on the presence of NOS in amphibians, indicate a considerable degree of phylogenetic conservation of the NO pathway amongst vertebrates.

Effect of acute and repeated restraint stress on glucose oxidation to CO2 in hippocampal and cerebral cortex slices

It has been suggested that glucocorticoids released during stress might impair neuronal function by decreasing glucose uptake by hippocampal neurons. Previous work has demonstrated that glucose uptake is reduced in hippocampal and cerebral cortex slices 24 h after exposure to acute stress, while no effect was observed after repeated stress. Here, we report the effect of acute and repeated restraint stress on glucose oxidation to CO2 in hippocampal and cerebral cortex slices and on plasma glucose and corticosterone levels. Male adult Wistar rats were exposed to restraint 1 h/day for 50 days in the chronic model. In the acute model there was a single exposure. Immediately or 24 h after stress, the animals were sacrificed and the hippocampus and cerebral cortex were dissected, sliced, and incubated with Krebs buffer, pH 7.4, containing 5 mM glucose and 0.2 µCi D-[U-14C] glucose. CO2 production from glucose was estimated. Trunk blood was also collected, and both corticosterone and glucose were measured. The results showed that corticosterone levels after exposure to acute restraint were increased, but the increase was smaller when the animals were submitted to repeated stress. Blood glucose levels increased after both acute and repeated stress. However, glucose utilization, measured as CO2 production in hippocampal and cerebral cortex slices, was the same in stressed and control groups under conditions of both acute and chronic stress. We conclude that, although stress may induce a decrease in glucose uptake, this effect is not sufficient to affect the energy metabolism of these cells.