Aims: Effects of salt stress on the physiology of Salvinia auriculata were investigated. Method Plants were supplemented with 0, 50, 100 and 150 mmol L-1 NaCl and incubated for 5 days. NO content was evaluated after 2 hours and 5 days. Photosynthetic pigments, proline and nutrients were analyzed after 5 days. Major Results Higher chlorophyll a content was observed in plants treated with 50 mmol L-1, decreasing in higher NaCl concentrations, while chorophyll b content decreased with increasing NaCl concentrations. Exposure to 50 mmol L-1 NaCl increased biomass, while higher concentrations caused loss of biomass. Ca, K and Mg decreased with increasing NaCl concentrations, and the Na/K ratio was significantly increased at 150 mmol L-1 NaCl. Proline increased significantly at 150 mmol L-1. Extracellular NO content increased after 2 hours, with significantly higher NO concentrations in roots observed at 50 mmol L-1. Decreases in NO content were observed after 5 days. Conclusions The results indicate that moderate salinity induces NO production earlier during incubation, probably associated to signaling for the production of compounds that assist in stress tolerance. At higher concentrations, this tolerance is reduced. This allows for further understanding of the physiological and biochemical mechanisms associated with the adaptation of this macrophyte to saline conditions, which, in turn, affect this species ecology and distribution in coastal areas.

AIM: This study aimed to investigate the effects of NaCI and Na2So4 salts on Ca, CI, K, Mg N, P, S and Na content as well as on the content of photosynthetic pigments (chlorophyll-a, chlorophyll-b and carotenoids), proline content and on the foliar morphology of Salvinia auriculata Aubl. METHODS: The plants were collected in Jacu lagoon, located in the North of Rio de Janeiro State, and after a five-day-acclimation period, experiments were performed in the greenhouse with 0, 100, 200 mM concentrations of NaCI and Na2SO4 salts and the usual techniques for light and electron microscopy. RESULTS: After seven days of experiment, a decrease in the content of Ca2+, K+, Mg2+, P, N ions as well as in the content of photosynthetic pigments (chlorophyll-a,b and carotenoids) in Salvinia auriculata under saline treatments was observed. The proline content showed an upward tendency as compared to the control. Under transmission electron microscopy, it was observed that, on the foliar limb, there was a membrane system disorder, mainly of chloroplasts, with higher presence of starch grains of plant cells subjected to salinity. Under scanning electron microscope, the integrity of trichomes and foliar limb cells of Salvinia auriculata subjected to the control treatment as well as the changes caused by salinization on the surface of cells were observed. CONCLUSION: As for all the salinization effects evaluated, it was noticed that the increase in Na2SO4 salt concentration resulted in higher morphological and nutritional alterations in the floating aquatic macrophyte, Salvinia auriculata.

AIM: To evaluate, in a short-time exposure, the physiological responses of Salvinia auriculata Aubl. under different concentrations of Cu. METHODS: The plants were exposed to treatments with 0.01, 0.1, 1 and 10 mM of Cu in a period of 2 days. Then development variables of S. auriculata (weight, photosynthetic pigments, and soluble carbohydrate), lipid peroxidation (malondialdehyde, aldehydes, and electrolyte leakage) and production of antioxidants (anthocyanins, carotenoids, flavonoids, and proline) were evaluated. RESULTS: It was observed fresh weight reductions in concentrations above 1 mM of Cu. Chlorophyll a decreased with the increase of Cu concentrations unlike chlorophyll b. The ratio chlorophyll a / chlorophyll b was changed due to the degradation of photosynthetic pigments. The reductions of carotenoids were more pronounced than that of total chlorophyll. The values of electrolyte leakage ranged from 14 to 82 % and lipid peroxidation from 7 to 46 nmol.g-1. Flavonoids and soluble carbohydrates showed reductions with the increase of Cu concentration. Anthocyanins, phenolic compounds, and proline when subjected to 0.1 mM of Cu had increased, suggesting adaptability of plant stress caused directly by metal and reactive oxygen species. In higher concentrations, degradation and/or direct modifications of these molecules possibly occurred. CONCLUSIONS: The data suggest that S. auriculata is provided with an efficient mechanism against stress caused by Cu in the concentration of 0.1 mM. As for higher concentrations (1 and 10 mM), despite its role as micronutrients, Cu was toxic to the plant due to the redox behavior of this metal, which leads to the exacerbated formation of reactive oxygen species, inducing to severe damage such as biological membrane degradation and protein denaturation.