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.

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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.

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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.