RESUMO
In this study, two cyanobacterial strains (morphologically identified as Microcystis novacekii BA005 and Nostoc paludosum BA033) were exposed to different Mn concentrations: 7.0, 10.5, 15.7, 23.6 and 35.4 mg L-1 for BA005; and 15.0, 22.5, 33.7, 50.6, and 76.0 mg L-1 for BA033. Manganese toxicity was assessed by growth rate inhibition (EC50), chlorophyll a content, quantification of Mn accumulation in biomass and monitoring morphological and ultrastructural effects. The Mn EC50 values were 16 mg L-1 for BA005 and 39 mg L-1 for BA033, respectively. Reduction of chlorophyll a contents and ultrastructural changes were observed in cells exposed to Mn concentrations greater than 23.6 and 33.7 mg L-1 for BA005 and BA033. Damage to intrathylakoid spaces, increased amounts of polyphosphate granules and an increased number of carboxysomes were observed in both strains. In the context of the potential application of these strains in bioremediation approaches, BA005 was able to remove Mn almost completely from aqueous medium after 96 h exposure to an initial concentration of 10.5 mg L-1, and BA033 was capable of removing 38% when exposed to initial Mn concentration of 22.5 mg L-1. Our data shed light on how these cyanobacterial strains respond to Mn stress, as well as supporting their utility as organisms for monitoring Mn toxicity in industrial wastes and potential bioremediation application.
Assuntos
Manganês/efeitos adversos , Microcystis/efeitos dos fármacos , Nostoc/efeitos dos fármacos , Poluentes Químicos da Água/efeitos adversos , Biodegradação Ambiental , Microcystis/fisiologia , Microcystis/ultraestrutura , Microscopia Eletrônica de Transmissão , Nostoc/fisiologia , Nostoc/ultraestrutura , Tilacoides/efeitos dos fármacos , Tilacoides/ultraestruturaRESUMO
In the search for natural inhibitors of plant growth, we investigate the mechanism of action of the natural furoquinoline alkaloids isolated from Balfourodendron riedelianum (Rutaceae): evolitrine (1), kokusaginine (2), γ-fagarine (3), skimmianine (4) and maculosidine (5) on the photosynthesis light reactions. Their effect on the electron transport chain on thylakoids was analyzed. Alkaloids 1, 2, 4 and 5 inhibited ATP synthesis, basal, phosphorylating and uncoupled electron transport acting as Hill reaction inhibitors on spinach chloroplasts. Alkaloid 3 was not active. The inhibition and interaction site of alkaloids 1, 2, 4 and 5 on the non-cyclic electron transport chain was studied by polarography and fluorescence of the chlorophyll a (Chl a). The results indicate that the target for 1 was localized on the donor and acceptor side of PS II. In addition alkaloids 2 and 5 affect the PS I electron acceptors on leaf discs.
Assuntos
Alcaloides/isolamento & purificação , Alcaloides/farmacologia , Cloroplastos/metabolismo , Fotossíntese/efeitos dos fármacos , Quinolinas/química , Rutaceae/química , Spinacia oleracea/citologia , Trifosfato de Adenosina/biossíntese , Alcaloides/química , Sítios de Ligação , Clorofila/metabolismo , Clorofila A , Cloroplastos/efeitos dos fármacos , Transporte de Elétrons/efeitos dos fármacos , Complexo de Proteína do Fotossistema II/metabolismo , Folhas de Planta/citologia , Folhas de Planta/enzimologia , Folhas de Planta/metabolismo , Spinacia oleracea/enzimologia , Spinacia oleracea/metabolismo , Tilacoides/efeitos dos fármacos , Tilacoides/metabolismoRESUMO
Three compounds were isolated from Maytenus acanthophylla Reissek (Celastraceae): the pentacyclic triterpenes lup-20(29)-en-3ß-ol (lupeol, 1) and 3ß-lup-20(29)-en-3-yl acetate (2) and the carbohydrate 1,2,3,4,5,6-hexa-O-acetyldulcitol (3); lupeol was also isolated from Xylosma flexuosa. The compounds' structures were elucidated by spectroscopic and spectrometric analysis. Compound 1 acts as an energy transfer inhibitor, interacting with isolated CF1 bound to thylakoid membrane, and dulcitol hexaacetate 3 behaves as a Hill reaction inhibitor and as an uncoupler, as determined by polarography. Chlorophyll a (Chl a) fluorescence induction kinetics from the minimum yield F0 to the maximum yield F(M )provides information of the filling up from electrons coming from water to plastoquinone pool with reducing equivalents. In this paper we have examined the effects of compounds 1 and 3 on spinach leaf discs. Compound 1 induces the appearance of a K-band, which indicates that it inhibits the water splitting enzyme. In vivo assays measuring the fluorescence of chl a in P. ixocarpa leaves sprayed with compound 1, showed the appearance of the K-band and the PSII reaction centers was transformed to "heat sinks" or silent reaction centers unable to reduce Q(A). However, 3 also induced the appearance of a K band and a new band I appears in P. ixocarpa plants, therefore it inhibits at the water splitting enzyme complex and at the PQH2 site on b6f complex. Compounds 1 and 3 did not affect chlorophyll a fluorescence of L. perenne plants.
Assuntos
Galactitol/farmacologia , Luz , Fotossíntese/efeitos dos fármacos , Fotossíntese/efeitos da radiação , Triterpenos/farmacologia , ATPase de Ca(2+) e Mg(2+)/metabolismo , Clorofila/metabolismo , Clorofila A , Transporte de Elétrons/efeitos dos fármacos , Transporte de Elétrons/efeitos da radiação , Fluorescência , Galactitol/química , Cinética , Maytenus/química , Paraquat/metabolismo , Triterpenos Pentacíclicos/química , Triterpenos Pentacíclicos/farmacologia , Fosforilação/efeitos dos fármacos , Fosforilação/efeitos da radiação , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/efeitos da radiação , Spinacia oleracea/efeitos dos fármacos , Spinacia oleracea/metabolismo , Spinacia oleracea/efeitos da radiação , Tilacoides/efeitos dos fármacos , Tilacoides/enzimologia , Tilacoides/efeitos da radiação , Triterpenos/químicaRESUMO
Four natural products were isolated from the fungus Botryosphaeria rhodina, and their effects on photosynthesis were tested. Only lasiodiplodin (1) inhibited ATP synthesis and electron flow from water to methylviologen; therefore, it acts as a Hill reaction inhibitor in freshly lysed spinach thylakoids. Photosystem I and II and partial reactions as well as ATPase were measured in the presence of 1. Three new different sites of 1 interaction and inhibition were found: one at CF1, the second in the water-splitting enzyme, and the third at the electron-transfer path between P680 and QA; these targets are different from that of the synthetic herbicides present. Electron transport chain inhibition by 1 was corroborated by fluorescence induction kinetics studies.
Assuntos
Ascomicetos/química , Fotofosforilação/efeitos dos fármacos , Tilacoides/efeitos dos fármacos , Tilacoides/metabolismo , Zearalenona/análogos & derivados , Adenosina Trifosfatases/antagonistas & inibidores , Trifosfato de Adenosina/biossíntese , Transporte de Elétrons/efeitos dos fármacos , Inibidores Enzimáticos/farmacologia , Folhas de Planta/ultraestrutura , Spinacia oleracea/ultraestrutura , Zearalenona/química , Zearalenona/farmacologiaRESUMO
In our search for new natural photosynthetic inhibitors that could lead to the development of "green herbicides" less toxic to environment, the diterpene labdane-8alpha,15-diol (1) and its acetyl derivative (2) were isolated for the first time from Croton ciliatoglanduliferus Ort. They inhibited photophosphorylation, electron transport (basal, phosphorylating and uncoupled) and the partial reactions of both photosystems in spinach thylakoids. Compound 1 inhibits the photosystem II (PS II) partial reaction from water to Na(+) Silicomolibdate (SiMo) and has no effect on partial reaction from diphenylcarbazide (DPC) to 2,6-dichlorophenol indophenol (DCPIP), therefore 1 inhibits at the water splitting enzyme and also inhibits PS I partial reaction from reduced phenylmetasulfate (PMS) to methylviologen (MV). Thus, it also inhibits in the span of P(700) to Iron sulfur center X (F(X)). Compound 2 inhibits both, the PS II partial reactions from water to SiMo and from DPC to DCPIP; besides this, it inhibits the photosystem I (PS I) partial reaction from reduced PMS to MV. With these results, we concluded that the targets of the natural product 2 are located at the water splitting enzyme, and at P(680) in PS II and at the span of P(700) to F(X) in PS I. The results of compounds 1 and 2 on PS II were corroborated by chlorophyll a fluorescence.
Assuntos
Croton/química , Diterpenos/farmacologia , Complexo de Proteína do Fotossistema I/antagonistas & inibidores , Complexo de Proteína do Fotossistema II/antagonistas & inibidores , Clorofila/química , Clorofila A , Diterpenos/química , Diterpenos/isolamento & purificação , Transporte de Elétrons/efeitos dos fármacos , Fotofosforilação/efeitos dos fármacos , Fotossíntese/efeitos dos fármacos , Extratos Vegetais/química , Spinacia oleracea/efeitos dos fármacos , Spinacia oleracea/metabolismo , Tilacoides/efeitos dos fármacos , Tilacoides/metabolismoRESUMO
Chromium is a highly toxic non-essential metal for microorganisms and plants. Due to its widespread industrial use, chromium (Cr) has become a serious pollutant in diverse environmental settings. The presence of Cr leads to the selection of algal populations able to tolerate high levels of Cr compounds. The diverse Cr-resistance mechanisms displayed by microorganisms include biosorption, diminished accumulation, precipitation, reduction of Cr(6+) to Cr(3+), and chromate efflux. In this paper we describe the effects of Cr(6+) (the more toxic species) on the photosynthetic and photoreceptive apparatus of the fresh water unicellular alga Chlamydomonas reinhardtii. We measured the effect of the heavy metal by means of in vivo absorption microspectroscopy of both the thylakoid compartments and the eyespot. The decomposition of the overall absorption spectra in pigment constituents indicates that Cr(6+) induced a complete pheophinitization of the chrorophylls and a modification of the carotenoids present in the eyespot only when its concentration is equal or greater than 10 microM. Due to this low tolerance level, C. reinhardtii could be used as indicator of Cr pollution, but it is not feasible for bioremediation purposes.
Assuntos
Chlamydomonas reinhardtii/efeitos dos fármacos , Cromo/toxicidade , Poluentes Químicos da Água/toxicidade , Animais , Chlamydomonas reinhardtii/metabolismo , Clorofila/metabolismo , Clorofila A , Fotossíntese/efeitos dos fármacos , Tilacoides/efeitos dos fármacos , Tilacoides/metabolismoRESUMO
Nineteen 2-[(R-phenyl)amine]-1,4-naphthalendione derivatives (PAN) were tested on spinach thylakoids for their activity as electron acceptors. These molecules act as photosystem I electron acceptors in the micromolar range. AC(50) values varied from 5 nM to 24 microM. QSAR analysis revealed a linear correlation of the m-PAN derivative log [1/AC(50)] with the energy difference of the LUMO and HOMO orbitals. The biological activity of p-PAN derivatives correlates linearly with structural parameters. Electron affinity is being the most important. The half wave I potential values (E(1/2)) of PAN compounds (from -213 to -569 mV vs. NHE) match with the mid-point potentials of the A(0) to F(X) niche of PSI electron transport carriers. The logP values of PAN derivatives were 3.35 and 3.88, indicating that they are hydrophobic compounds. Therefore PAN compounds accept electrons at the hydrophobic A(0) to F(X) niche of PSI.
Assuntos
Naftoquinonas/química , Naftoquinonas/farmacologia , Complexo de Proteína do Fotossistema I/efeitos dos fármacos , Complexo de Proteína do Fotossistema I/metabolismo , Trifosfato de Adenosina/biossíntese , Transporte de Elétrons/efeitos dos fármacos , Isomerismo , Cinética , Naftoquinonas/metabolismo , Fotobiologia , Relação Quantitativa Estrutura-Atividade , Spinacia oleracea/efeitos dos fármacos , Spinacia oleracea/metabolismo , Tilacoides/efeitos dos fármacos , Tilacoides/metabolismoRESUMO
The frequency of cyanobacterial blooms has been increasing all over the world. These blooms are often toxic and have become a serious health problem. The aim of this work was to search for population density control mechanisms that could inhibit the proliferation of the toxic bloom-forming genus Microcystis. Microcystis PCC 7806 cultured for long periods in liquid ASM-1 medium loses its characteristic green colour. When a medium of chlorotic cultures is added to a nutrient-replete culture, cell density increase is drastically reduced when compared with controls. Inhibition of cell proliferation occurs in Microcystis cultures from any growth stage and was not strain-specific, but other genera tested showed no response. Investigations on the mechanism of growth inhibition showed that cultures treated with the conditioned medium acquired a pale colour, with pigment concentration similar to that found in chlorotic cultures. Ultrastructural examination showed that the conditioned medium induced thylakoid membrane disorganization, typical of chlorotic cells, in nutrient-replete cultures. An active extract was obtained and investigations showed that activity was retained after heating and after addition of an apolar solvent. This indicates that activity of the conditioned medium from chlorotic cells results from non-protein, apolar compound(s).