RESUMO
Greenhouse experiments were carried out aiming to characterize-morphologically and biochemically-resistant and susceptible plants of C. sumatrensis. Two experiments were carried out to evaluate the behavior of morphological variables such as leaf area, height, and dry biomass weight, without application of paraquat (1,1'-dimethyl-4,4'-bipyridinium dichloride). Other experiments were conducted with two rates of paraquat application (0 and 800 g a.i ha-1); physiological variables were assessed at 2, 4, and 24 h after application (HAA), and plants were collected at 4 HAA for biochemical analyses of antioxidant enzymes and cell membrane peroxidation level. Without herbicide application, paraquat-resistant populations had higher dry biomass, leaf area, liquid photosynthetic rate, carboxylation efficiency, and stomatal conductance. The recovery of the photosynthetic apparatus by resistant plants after paraquat application is rapid (16 HAA) and, in general, presents physiological improvements in terms of photosynthetic rate and carboxylation efficiency. After paraquat treatment, the antioxidant system enzymes of resistant plants showed increased activity and decreased membrane peroxidation, indicating that these enzymes play an important role in the resistance mechanism of these plants.
Assuntos
Conyza , Herbicidas , Paraquat/metabolismo , Conyza/metabolismo , Antioxidantes/metabolismo , Brasil , Herbicidas/metabolismoRESUMO
Botryococcus braunii (B. braunii) is a green microalga primarily found in freshwater, reservoirs, and ponds. Photosynthetic pigments from algae have shown many bioactive molecules with therapeutic potential. Herein, we report the purification, characterization, and anticancer properties of photosystem I light-harvesting complex I (PSI-LHCI) from the green microalga B. braunii UTEX2441. The pigment-protein complex was purified by sucrose density gradient and characterized by its distinctive peaks using absorption, low-temperature (77 K) fluorescence, and circular dichroism (CD) spectroscopic analyses. Protein complexes were resolved by blue native-PAGE and two-dimensional SDS-PAGE. Triple-negative breast cancer MDA-MB-231 cells were incubated with PSI-LHCI for all of our experiments. Cell viability was assessed, revealing a significant reduction in a time- and concentration-dependent manner. We confirmed the internalization of PSI-LHCI within the cytoplasm and nucleus after 12 h of incubation. Cell death mechanism by oxidative stress was confirmed by the production of reactive oxygen species (ROS) and specifically superoxide. Furthermore, we monitored autophagic flux, apoptotic and necrotic features after treatment with PSI-LHCI. Treated MDA-MB-231 cells showed positive autophagy signals in the cytoplasm and nucleus, and necrotic morphology by the permeabilization of the cell membrane. Our findings demonstrated for the first time the cytotoxic properties of B. braunii PSI-LHCI by the induction of ROS and autophagy in breast cancer cells.
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Photosystem-inhibiting herbicides, such as diquat, act by inducing oxidative stress. However, oxidative damage impairs translocation, resulting in regrowth of the plants. The aim was to evaluate the effectiveness of diquat in controlling the growth of sourgrass exposed to different periods of darkness after application of the herbicide, as well as to evaluate the photosynthetic activity and the production of reactive oxygen species. Two experiments (field and greenhouse) were conducted by applying diquat (200 g a.i. ha-1) on sourgrass plants at the 3 to 4 tiller stage. The treated plants were subjected to different periods of darkness after diquat application (0, 1, 2, 3, 4, 5, and 6 h), in addition to the control treatment without any application. Growth inhibition and mass evaluations of the sourgrass plants were performed in both experiments, whereas photosynthetic activity and H2O2 accumulation in the leaves were evaluated in the greenhouse experiment. The results showed an increase in the sourgrass growth inhibition with an increase in the period of darkness after application. There was a need for a minimum of 6 h of darkness after diquat application to fully inhibit growth (100%) of the sourgrass, whereas plants that remained in the sun since application exhibited less than 50% inhibition. The increase in the period of darkness after diquat application resulted in a reduction in photosynthetic activity and, consequently, lower accumulation of H2O2. Thus, the maintenance of sourgrass in the dark for at least 6 h enables total control of the growth of the plants, preventing regrowth.
Assuntos
Estresse Oxidativo , Digitaria/crescimento & desenvolvimento , Controle de Plantas Daninhas , HerbicidasRESUMO
En la región amazónica, los sistemas agroforestales (SAFs) se recomiendan como una alternativa de producción sustentable para las comunidades locales. Un componente común en los SAFs amazónicos son los árboles frutales tropicales, que pueden formar parte del dosel o crecer en el sotobosque. En este trabajo, estudiamos el efecto de la radiación alta sobre la fotosíntesis, el crecimiento y la supervivencia de cuatro especies de árboles frutales amazónicos: Theobroma cacao, Eugenia stipitata, Inga edulis y Psidium guajava. Se midieron el crecimiento, fluorescencia de clorofila, intercambio de gases y pigmentos foliares en plántulas de cada especie que crecieron durante 12 meses dentro de casa-mallas en baja (8%), media (30%) y alta iluminación relativa (100%). Eugenia stipitata y T. cacao tuvieron la menor capacidad de aclimatación a la radiación solar alta, seguidas por I. edulis. En consecuencia, esas especies deben sembrarse bajo niveles de luz intermedia, para protegerlas del sol directo en las etapas iniciales de crecimiento. En contraste, las plántulas de P. guajava mostraron alta tolerancia a la elevada radiación solar, por lo que esta especie puede ser plantada bajo libre exposición solar.(AU)
In the Amazon region, agroforestry systems (AFSs) are recommended as a sustainable production alternative for local communities. A common component in Amazonian AFSs are tropical fruit trees, which can form the canopy or grow in the understory. In this study, we evaluated the effect of high radiation on photosynthesis, growth and seedling survival of four Amazonian fruit-tree species: Theobroma cacao, Eugenia stipitata, Inga edulis and Psidium guajava. Growth, chlorophyll fluorescence, gas exchange, and leaf pigments were measured in seedlings of each species grown for 12 months inside shade houses with low (8%), medium (30%) and high relative illumination (100%). Eugenia stipitata and T. cacao had the lowest acclimation capacity to high solar radiation, followed by I. edulis. Therefore, these species must be grown under intermediate light levels in early growth stages, to protect them from direct sunlight. In contrast, P. guajava seedlings demonstrated high tolerance to elevated radiation, therefore, this species can be planted under full sunlight.(AU)
Assuntos
Cacau/citologia , Cacau/crescimento & desenvolvimento , Eugenia/citologia , Eugenia/crescimento & desenvolvimento , Psidium/citologia , Psidium/crescimento & desenvolvimento , Carotenoides/análise , Cloroplastos , Complexo de Proteína do Fotossistema IIRESUMO
Photosynthesis involves the conversion of sunlight energy into stored chemical energy, which is achieved through electron transport along a series of redox reactions. Excess photosynthetic electron transport might be dangerous due to the risk of molecular oxygen reduction, generating reactive oxygen species (ROS) over-accumulation. Avoiding excess ROS production requires the rate of electron transport to be coordinated with the capacity of electron acceptors in the chloroplast stroma. Imbalance between the donor and acceptor sides of photosystem I (PSI) can lead to inactivation, which is called PSI photoinhibition. We used a light-inducible PSI photoinhibition system in Arabidopsis thaliana to resolve the time dynamics of inhibition and to investigate its impact on ROS production and turnover. The oxidation state of the PSI reaction center and rates of CO2 fixation both indicated strong and rapid PSI photoinhibition upon donor side/acceptor side imbalance, while the rate of inhibition eased during prolonged imbalance. PSI photoinhibition was not associated with any major changes in ROS accumulation or antioxidant activity; however, a lower level of lipid oxidation correlated with lower abundance of chloroplast lipoxygenase in PSI-inhibited leaves. The results of this study suggest that rapid activation of PSI photoinhibition under severe photosynthetic imbalance protects the chloroplast from over-reduction and excess ROS formation.
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Chlorophyll (Chl) loss is the main visible symptom of senescence in leaves. The initial steps of Chl degradation operate within the chloroplast, but the observation that 'senescence-associated vacuoles' (SAVs) contain Chl raises the question of whether SAVs might also contribute to Chl breakdown. Previous confocal microscope observations (Martínez et al., 2008) showed many SAVs containing Chl. Isolated SAVs contained Chl a and b (with a Chl a/b ratio close to 5) and lower levels of chlorophyllide a. Pheophytin a and pheophorbide a were formed after the incubation of SAVs at 30°C in darkness, suggesting the presence of Chl-degrading activities in SAVs. Chl in SAVs was bound to a number of 'green bands'. In the most abundant green band of SAVs, Western blot analysis showed the presence of photosystem I (PSI) Chl-binding proteins, including the PsaA protein of the PSI reaction center and the apoproteins of the light-harvesting complexes (Lhca 1-4). This was confirmed by: (i) measurements of 77-K fluorescence emission spectra showing a single emission peak at around 730 nm in SAVs; (ii) mass spectrometry of the most prominent green band with the slowest electrophoretic mobility; and (iii) immunofluorescence detection of PsaA in SAVs observed through confocal microscopy. Incubation of SAVs at 30°C in darkness caused a steady decrease in PsaA levels. Overall, these results indicate that SAVs may be involved in the degradation of PSI proteins and their associated chlorophylls during the senescence of leaves.
Assuntos
Clorofila/metabolismo , Cloroplastos/metabolismo , Nicotiana/metabolismo , Complexo de Proteína do Fotossistema I/metabolismo , Folhas de Planta/metabolismo , Proteínas de Plantas/metabolismo , Vacúolos/metabolismo , Envelhecimento , Senescência Celular , Escuridão , Plastídeos/metabolismo , ProteóliseRESUMO
The development of oxygenic photosynthesis by primordial cyanobacteria ~2.7 billion years ago led to major changes in the components and organization of photosynthetic electron transport to cope with the challenges of an oxygen-enriched atmosphere. We review herein, following the seminal contributions as reported by Jaganathan et al. (Functional genomics and evolution of photosynthetic systems, vol 33, advances in photosynthesis and respiration, Springer, Dordrecht, 2012), how these changes affected carriers and enzymes at the acceptor side of photosystem I (PSI): the electron shuttle ferredoxin (Fd), its isofunctional counterpart flavodoxin (Fld), their redox partner ferredoxin-NADP+ reductase (FNR), and the primary PSI acceptors F x and F A/F B. Protection of the [4Fe-4S] centers of these proteins from oxidative damage was achieved by strengthening binding between the F A/F B polypeptide and the reaction center core containing F x, therefore impairing O2 access to the clusters. Immobilization of F A/F B in the PSI complex led in turn to the recruitment of new soluble electron shuttles. This function was fulfilled by oxygen-insensitive [2Fe-2S] Fd, in which the reactive sulfide atoms of the cluster are shielded from solvent by the polypeptide backbone, and in some algae and cyanobacteria by Fld, which employs a flavin as prosthetic group and is tolerant to oxidants and iron limitation. Tight membrane binding of FNR allowed solid-state electron transfer from PSI bridged by Fd/Fld. Fine tuning of FNR catalytic mechanism led to formidable increases in turnover rates compared with FNRs acting in heterotrophic pathways, favoring Fd/Fld reduction instead of oxygen reduction.
Assuntos
Evolução Molecular , Ferredoxina-NADP Redutase/metabolismo , Ferredoxinas/metabolismo , Flavodoxina/metabolismo , Complexo de Proteína do Fotossistema I/metabolismo , Fotossíntese , Processos FototróficosRESUMO
The inactivation of the chloroplast ascorbate peroxidases (chlAPXs) has been thought to limit the efficiency of the water-water cycle and photo-oxidative protection under stress conditions. In this study, we have generated double knockdown rice (Oryza sativa L.) plants in both OsAPX7 (sAPX) and OsAPX8 (tAPX) genes, which encode chloroplastic APXs (chlAPXs). By employing an integrated approach involving gene expression, proteomics, biochemical and physiological analyses of photosynthesis, we have assessed the role of chlAPXs in the regulation of the protection of the photosystem II (PSII) activity and CO2 assimilation in rice plants exposed to high light (HL) and methyl violagen (MV). The chlAPX knockdown plants were affected more severely than the non-transformed (NT) plants in the activity and structure of PSII and CO2 assimilation in the presence of MV. Although MV induced significant increases in pigment content in the knockdown plants, the increases were apparently not sufficient for protection. Treatment with HL also caused generalized damage in PSII in both types of plants. The knockdown and NT plants exhibited differences in photosynthetic parameters related to efficiency of utilization of light and CO2. The knockdown plants overexpressed other antioxidant enzymes in response to the stresses and increased the GPX activity in the chloroplast-enriched fraction. Our data suggest that a partial deficiency of chlAPX expression modulate the PSII activity and integrity, reflecting the overall photosynthesis when rice plants are subjected to acute oxidative stress. However, under normal growth conditions, the knockdown plants exhibit normal phenotype, biochemical and physiological performance.