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A fotossíntese é um processo essencial para a manutenção da vida, pois permite aos seres clorofilados a produção de matéria orgânica e o fornecimento de oxigênio para à atmosfera. Apesar da sua relevância, muitos estudantes apresentam dificuldades para compreender os processos bioquímicos da fotossíntese. Assim, cria-se uma barreira no processo de ensino e aprendizagem que necessita ser superada através de metodologias eficientes. Os modelos didáticos revelam-se eficazes na construção de conhecimentos complexos ao permitirem a representação da realidade de forma simplificada. Neste sentido, esse trabalho teve por objetivo desenvolver modelos didáticos dinâmicos sobre o processo fotossintético e aplicá-los para estudantes do ensino médio da rede estadual de ensino do município de Juiz de Fora-MG. Os resultados foram positivos, pois demonstraram maior compreensão e interesse dos estudantes em relação à fotossíntese, além da desconstrução de conceitos errôneos referentes a esse conteúdo.

Glutathione is essential for plant tolerance to arsenic but few studies have focused on the coordination between the enzymes involved in its metabolism. We exposed Pistia stratiotes to four treatme...

Phytoremediation is considered an ecologically beneficial technique for removing arsenic from aquatic environments but studies on the mechanisms of tolerance to this pollutant, when present in the form of arsenite (AsIII) still need to be performed. Thus, in order to evaluate the potential of Pistia stratiotes to phytoremediation of AsIII and the morphological and biochemical responses involved in metalloid tolerance, P. stratiotes plants were exposed to four treatments: 0 (control), 5, 10 and 20 µM AsIII, remaining under treatment for 24 h for biochemical analysis and for 4 days to analyze the arsenic (As) uptake, biomass production, bioconcentration factor (BCF), translocation factor (TF) and visual symptomatology. The plants were able to accumulate As in both roots and leaves. This accumulation was higher in the treatment with 10 µM AsIII (1120.40 and 31.60 µg g−1 dry weight in roots and leaves, respectively), decreasing in the following concentration. P. stratiotes also showed a high BCF, that was higher than 1000 when exposed to 5 and 10 µM AsIII (1808.38 and 1536.02, respectively). The pollutant was maintained mainly at the root (TF was always lower than 1.0) which may be a defense mechanism of aquatic plants to As. Despite the significant accumulation of pollutant, the plants were able to maintain growth in all evaluated concentrations, although in very different proportions. In fact, while in the lower concentration of As the biomass production was not affected, in the treatment with 20 μM AsIII the dry biomass decreased in approximately 77%. The accumulation of As resulted in the appearance of visual symptoms of toxicity such as chlorosis, darkening and reduction of the root system, which were more conspicuous in the highest As concentration. The metalloid exposition also triggered biochemical alterations, increasing the membrane damage and the reactive oxygen species (ROS) levels and, once again, these damages were more intense in the plants exposed to 20 μM AsIII. The action of the antioxidant system (especially in the leaves) and the compartmentalization of the pollutant in the root system apparently was important in the P. stratiotes response to toxic compounds and allowed the plants to maintain the cell homeostasis and the growth at the two lowest As concentrations. Thus, the data suggest that P. stratiotes may has a potential for phytoremediation of aquatic environments contaminated with AsIII concentrations close to 10 µM.

Nitric oxide increased lettuce’s tolerance to salinity by restoring its hormonal balance, consequently reducing Na + accumulation and activating defense mechanisms that allowed the attenuation of ionic, oxidative, and osmotic stresses. Agricultural crops are continually threatened by soil salinity. The plant’s ability to tolerate soil salinity can be increased by treatment with the signaling molecule nitric oxide (NO). Involvement of NO in plant metabolism and its interactions with phytohormones have not been fully described, so knowledge about the role of this radical in signaling pathways remains fragmented. In this work, Lactuca sativa (lettuce) plants were subjected to four treatments: (1) control (nutrient solution); (2) SNP [nutrient solution containing 70 μM sodium nitroprusside (SNP), an NO donor]; (3) NaCl (nutrient solution containing 80 mM NaCl); or (4) SNP + NaCl (nutrient solution containing SNP and NaCl). The plants were exposed to these conditions for 24 h, and then, the roots and leaves were collected and used to evaluate biochemical parameters (reactive oxygen species (ROS) production, cell membrane damage, cell death, antioxidant enzymes activities, and proline concentration), physiological parameters (pigments’ concentration and gas-exchange measurements), and phytohormone content. To evaluate growth, tolerance index, and nutrient concentration, the plants were exposed to the treatments for 3 days. L sativa exposure to NaCl triggered ionic, osmotic, and oxidative stress, which resulted in hormone imbalance, cell death, and decreased growth. These deleterious changes were correlated with Na+ content in the vegetative tissues. Adding NO decreased Na+ accumulation and stabilized the mineral nutrient concentration, which maintained the photosynthetic rate and re-established growth. NO-signaling action also re-established the phytohormones balance and resulted in antioxidant system activation and osmotic regulation, with consequent increase in plants tolerance to the salt.

Antioxidant enzymes are important components in the defense against arsenic (As) stress in plants. Here, we tested the hypothesis that Salvinia molesta, an aquatic fern, counteracts the harmful arsenite (AsIII) effects by activating scavenging reactive oxygen species (ROS) enzymes. Thus, our objective was to investigate the role of the superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), and ascorbate peroxidase (APX) in S. molesta tolerance to AsIII and indicate the use of this plant in remediation of contaminated water. Plants were grown in nutrient solution at pH 6.5 and exposed to 0, 5, 10, or 20 µM AsIII for 96 h (analyses of As absorption, mineral nutrient content, and relative growth rate) and for 24 h (analyses of oxidative stress indicators and enzymatic antioxidant defenses). In the floating leaves, there was a greater basal activity of the antioxidant enzymes and less accumulation of As than in submerged leaves. The submerged leaves, which function as roots in S. molesta, accumulated more As than floating leaves, and SOD and CAT activities were inhibited. Thus, there was a greater production of ROS and oxidative stress. Our results show that S. molesta presents enzymatic antioxidant defenses to alleviate AsIII toxicity and are more effectives in the floating leaves. These results are important to elucidate the AsIII tolerance mechanisms in S. molesta and the possibility of their use in contamined water phytoremediation. Additional studies exposing plants to more prolonged stress and using AsIII concentrations closer to those found in contaminated environments will confirm this claim.

In many plant species, tolerance to toxic metals is highly dependent on glutathione, an essential metabolite for cellular detoxifi cation. We evaluated the responses of glutathione metabolism to arsenite (As III ) in Salvinia molesta , an aquatic fern that has unexplored phytoremediation potential. Plants were exposed to diff erent As III concentrations in nutrient solution for 24 h. As III caused cell membrane damage to submerged leaves, indicating oxidative stress. Th ere was an increase in the glutathione content and ϒ-glutamylcysteine synthetase enzyme activity in the submerged and fl oating leaves. Th e glutathione peroxidase and glutathione sulfotransferase enzymes also showed increased activity in both plant parts, whereas glutathione reductase only showed increased activity in the submerged leaves. Th ese fi ndings suggest an important role for glutathione in the protection of S. molesta against the toxic eff ects of As III , with more eff ective tolerance responses in the fl oating leaves.

High arsenic (As) concentrations are toxic to all the living organisms and the cellular response to this metalloid requires the involvement of cell signaling agents, such as nitric oxide (NO). The As toxicity and NO signaling were analyzed in Pistia stratiotes leaves. Plants were exposed to four treatments, for 24 h: control; SNP [sodium nitroprusside (NO donor); 0.1 mg L-1]; As (1.5 mg L-1) and As + SNP (1.5 and 0.1 mg L-1, respectively). The absorption of As increased the concentration of reactive oxygen species and triggered changes in the primary metabolism of the plants. While photosynthesis and photorespiration showed sharp decrease, the respiration process increased, probably due to chemical similarity between arsenate and phosphate, which compromised the energy status of the cell. These harmful effects were reflected in the cellular structure of P. stratiotes, leading to the disruption of the cells and a possible programmed cell death. The damages were attenuated by NO, which was able to integrate central plant physiological processes, with increases in non-photochemical quenching and respiration rates, while the photorespiration level decreased. The increase in respiratory rates was essential to achieve cellular homeostasis by the generation of carbon skeletons and metabolic energy to support processes involved in responses to stress, as well to maintaining the structure of organelles and prevent cell death. Overall, our results provide an integrated view of plant metabolism in response to As, focusing on the central role of NO as a signaling agent able to change the whole plant physiology.

Nitric oxide (NO) is an important molecule involved in the perception of stress induced by toxic compounds such as arsenic (As). The present study investigated the role of NO applied as sodium nitroprusside (SNP) in cell signalling and the ability of NO to attenuate the toxic effects of As (in the form of sodium arsenate) in water hyacinth (Eichhornia crassipes). Water hyacinth plants were collected and assigned to one of the following treatments: control; 100 μM SNP; 20 μM As; or 20 μM As + 100 μM SNP. The plants remained under these conditions for 0, 4, 12, and 24 h. After each time interval, the plants were collected and As absorption, production of reactive oxygen species (ROS), integrity of membranes, and antioxidant enzyme activities were evaluated. The plants were able to absorb and accumulate large amounts of As, even after only four hours of exposure to the pollutant. The absorption and bioaccumulation factor of As was even greater when plants were exposed to both As and SNP. The accumulation of As triggered increases in ROS production and cell membrane damage. In the presence of SNP, the tolerance index to As increased and damage was mitigated. Therefore, from the present work, it was possible to conclude that exogenous NO influenced the ability of plants to tolerate As; this finding has implications for phytoremediation in areas contaminated by As.