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Efecto del arsénico sobre las propiedades ópticas y fotofísicas de plantas acuáticas Arsenic´s effect on optical and photophysical properties of aquatic plants Analia Iriel,1 Gavin Dundas,1 Alicia Fernández Cirelli,1 M. Gabriela Lagorio2 1 Centro de Estudios Transdisciplinarios del Agua, Facultad de Ciencias Veterinarias, Universidad de Buenos Aires, Av. Chorroarín 280, C1427CWO, Buenos Aires, Argentina, 2 INQUIMAE / Dpto. de Química Inorgánica, Analítica y Química Física. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Ciudad Universitaria. Pabellón II, 1er piso, C1428EHA, Buenos Aires, Argentina The main purpose of our work was to evaluate the effects of Arsenic on the optical and photophysical properties of leaves of different aquatic plants and to assess reflectance and fluorescence emission as indicators of Arsenic toxicity. An additional aim of this work was to evaluate the possibility of detecting photosystem damage through the interpretation of Chlorophyll fluorescence spectra. Three macrophytes: Lemna minor, Azolla filiculoides and Vallisneria gigantea were maintained in a solution of As(V) (2 ppm) or in As-free media (control) for a period of seven days. Reflectance spectra of the leaves were then obtained in a Shimadzu 3100 spectrophotometer equipped with an integrated sphere from 300 to 2400 nm. From these data, the remission function, F(R) (absorption spectrum) was calculated (1). Emission spectra of intact plants were obtained under low photon conditions on a PTI Model QM-1 spectrofluorometer with a front-facing arrangement. Prior to measurement, plants were dark-adapted for 15 minutes. Fluorescence spectra were recorded from 600 to 800 nm using an excitation wavelength of 460 nm and they were then corrected for light re-absorption processes (2).From these spectra, fluorescence ratios between red and far red maxima were calculated. Variable fluorescence was investigated using a pulse-modulated chlorophyll fluorometer (Hansatech FMS1), on dark-adapted leaves. From these last measurements, the quantum efficiency of PSII photochemistry was calculated (3). Absorption spectra for Lemna minor did not show any change upon As treatment. Azolla filiculoides and Vallisneria gigantea, instead, both increased absorption in the region from 400-500 nm in the presence of As. An increase around 530 nm was also present for Azolla filiculoides. This spectral behaviour could be related to an increase in the biosynthesis of flavonoids as a defensive response towards As action for Azolla and Vallisneria. The fluorescence ratio (red/Far-red) for As-treated samples did not vary in the case of Lemna minor and decreased for Azolla filiculoides and Vallisneria gigantea. This fact showed a relative decreased in the fluorescence of photosystem II compared to photosystem I emission, suggesting any kind of preferential damage in photosystem II for the two last species. Finally, the quantum efficiency of PSII photochemistry decreased around 25% for As treated leaves of Azolla filiculoides and Vallisneria gigantea. Similarly to what happened with other optical properties, the quantum efficiency of PSII photochemistry did not change appreciably for Lemna minor. Our experiments have demonstrated that reflectance and chlorophyll fluorescence are signals sensitive to As presence in certain aquatic plants. Preliminary results in our laboratory have shown that Vallisneria gigantea is the best As-absorbing species of the three aquatic plants studied. An accurate analysis of the content of Arsenic accumulated by each plant is under evaluation at the moment.. Referencias 1-Iriel, A., Lagorio, M. G., Photochem. Photobiol. Sci., 8, 337, 2009 2-Cordon, G. B., Lagorio, M. G., Photochem. Photobiol. Sci., 5, 735, 2006 3- Mendes Novo, J., Iriel, A., Lagorio, M. G.; Photochem. Photobiol. Sci., 11, 724, 2012 grafob2013@grupoargentinodefotobiologia.info.