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ResumoEm Calopogonium mucunoides, o metabolismo de nitrogênio foi signiicativamente alterado entre os diferentes estágios de desenvolvimento das plantas. Ao longo do ciclo de vida, mesmo na presença de nitrato, a planta manteve-se nodulada e altas concentrações de ureídeos foram identiicadas nos tecidos e seiva de xilema, evidência de que a espécie é tolerante ao nitrato e que este não afeta a ixação de nitrogênio ao longo do desenvolvimento. A redução bioquímica de nitrato apresenta alterações ao longo do ciclo de vida, com mudança no sítio de redução junto com mudanças na concentração de aminoácidos solúveis totais. No entanto, a atividade de nitrato redutase constitutiva em nódulos desaparece com a exposição ao nitrato. Palavras-chave: Leguminosa; Ureídeos; Nodulação AbstractNitrate inluences the metabolism of nitrogenous compounds in calopo (Calopogonium mucunoides) throughout the life cycle. In Calopogonium mucunoides, nitrogen metabolism was signiicantly altered between the various plant development stages. Throughout the life cycle, even in the presence of nitrate, the plant kept itself nodulated and high ureide concentrations were identiied in xylem tissues and sap, evidencing that the species is tolerant to nitrate and that this does not affect nitrogen ixation over development. Nitrate biochemical reduction presents alterations throughout the life cycle, with change in the reduction site along with changes in total soluble amino acid concentrations. However, constitutive reductase nitrate activity in nodules disappears with the exposition to nitrate.

Nitric oxide (NO) plays important role in alleviating abiotic stresses in plants, including those caused by arsenic (As). Here, we examined the effects of endogenous and exogenous NO in Spirodela intermedia W. Koch (Lemnaceae) under As exposure. For this purpose, we evaluated the As content, reactive oxygen species (ROS) levels, membrane damage and enzymatic antioxidant system. The levels of endogenous NO and the activity of nitrate reductase (NR) were also addressed. The As treatment triggered the production of high endogenous levels of NO and a pronounced activation of the antioxidant enzymes; however, it was not sufficient to completely avoid the increment in ROS content and membrane damage. In contrast, exogenous NO decreased the As levels in plants exposed to As and NO donor, mitigating the ROS production and membrane damage, while maintaining a lower activity of the antioxidant enzymes compared with As-treated plants. Exogenous NO further downregulated the NR activity by a negative feedback, while As boosted the NR activity, consistent with the high endogenous levels of NO observed upon As treatment. Our results suggest that both endogenous and exogenous NO play critical roles in alleviating the As-induced oxidative stress in S. intermedia by reducing As uptake, and possibly by acting as an antioxidant molecule.

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