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- Photosynthetic pigment laser-induced fluorescence indicators for the detection of changes associated with trace element stress in the diatom model species Phaeodactylum tricornutumPublication . Cabrita, Maria Teresa; Gameiro, C.; Utkin, Andrei B.; Duarte, Bernardo; Caçador, Isabel; Cartaxana, PauloThis work reports changes on cell number, growth rate, trace element content, chlorophyll a (Chl a) and carotenoid concentrations, and laser-induced fluorescence (LIF) spectra of Phaeodactylum tricornutum exposed to Co, Ni, Cu, Zn, Cd, Hg, Pb, and a mixture of all elements combined (Mix). The total levels of trace elements associated with the cells were significantly higher in the exposed than in control ones. Concomitantly, specific cell growth was significantly lower in exposed P. tricornutum, suggesting that trace elements affected the microalgae physiology. The LIF emission spectra showed two typical emission bands in red (683-698 nm) and far-red (725-730 nm) regions. Deviations in LIF spectra and changes in F685/F735 ratio were investigated as indicators of trace element-induced changes. Fluorescence intensity emitted by exposed microalgae decreased in far-red region when compared to control cells, suggesting Chl a damage and impairment of pigment biosynthesis pathways by trace elements, confirmed by Chl a and carotenoid concentration decrease. Significant increase in F685/F735 ratio was detected for all elements except Zn and more accentuated for Co, Hg, and Mix. Significant deviations in wavelength emission maxima in red region were also more significant (between 8 and 13 nm) for Co, Hg, and Mix. Growth changes agreed with deviations in LIF spectra and F685/F735 ratio, supporting their applicability as indicators. This study clearly shows F685/F735 ratio and the deviations in wavelength emission maxima as adequate trace element stress indicators and P. tricornutum as a promising biomonitor model species. LIF-based techniques can be used as time-saving, highly sensitive, and effective alternative tool for the detection of trace element stress, with potential for remote sensing and trace element contamination screening in marine coastal areas.
- Photochemical features and trace element substituted chlorophylls as early detection biomarkers of metal exposure in the model diatom Phaeodactylum tricornutumPublication . Cabrita, Maria Teresa; Duarte, Bernardo; Gameiro, C.; Godinho, Rita M.; Caçador, IsabelEstablishing marine species equipped with efficient biomarkers of trace element stress is a major requirement for the assessment of trace element contamination in marine ecosystems. This study investigates PS II overall activity and efficiency during light harvesting, electron transport chain (ETC) behaviour, OJIP-transient light curves, and pigment profiles, in the model marine diatom species Phaeodactylum tricornutum exposed to Cr, Co, Ni, Cu, Zn, Cd, Hg, Pb and to a mixture of all elements combined (Mix). OJIP-test parameters and trace element substituted chlorophylls were investigated as potential biomarkers of stress induced by trace elements. Hg-exposed cells showed a shift in balance towards PS I activity, promoted by increase in the electron transport from PQH2 to the reduction of PS I end electron acceptors. Other elements had more limited effects, mostly affecting energy dissipation and pigment levels to various degrees. Decoupling of PS II antennae connectivity was found in Co exposed cells. Chromium induced negative effects on PS I, but had no influence at the Oxygen Evolving Complexes (OECs) level. Copper caused a shift in the equilibrium between PS towards the PS I by reducing the PS II efficiency. Cadmium induced damage in OECs of the PS II donor side, but had no effect on the energy transduction pathway, maintaining energy processing efficiency. Lead had no significant effect on the energy transduction pathway, but produced changes at pigment level, leading to an increase in the chlorophyll and diadinoxanthin. In contrast, Ni had a beneficial role in P. tricornutum photochemistry, leading to increased number of available RC and oxidized quinone pool size, possibly because concentrations used were not able to induce severe cell damage. Copper, Cd and Zn led to substitution of Mg in chlorophyll a molecules, with the formation of less efficient CuChl a, CdChl a and ZnChl a. The biomarkers used evidenced the damaging effect of Co, Cu, Cr, Pb, Hg and all trace elements combined (Mix), pointing to Hg as the most harmful element. These physiological changes highlight P. tricornutum as a promising sentinel species for trace element contamination and the proposed photochemical features suitable as an efficient battery of biomarkers for trace element stress early detection in marine systems.