Abstract
We examined the responsiveness of unicellular green alga Dunalliela tertiolecta to selected stressors employing confocal- and time-resolved imaging of endogenous fluorescence. Our aim was to monitor cell endogenous fluorescence changes under exposure to heavy metal Cd, acidification, as well as light by laser-induced photobleaching. The accumulation of Cd in algae cells was confirmed by the secondary ion mass spectroscopy technique. For the first time, custom-made computational techniques were employed to evaluate separately the fluorescence in the flagella vs. the body region. In the presence of Cd, we recorded increase in the green fluorescence in the flagella region in the form of opacities, without change in the fluorescence lifetimes, suggesting higher availability of the fluorescent molecules. Under acidification, we noted significant rise in the green fluorescence in the flagella region, but associated with longer fluorescence lifetimes, pointing to changes in the algae environment. Photobleaching experiments corroborated gathered observations. Obtained data support a differential responsiveness of the flagella vs. the body region to stressors and enable us to better understand the pathophysiological changes of algal cells in culture under stress conditions.
Highlights
Pollution by heavy metals, acid rains, together with modification of illumination conditions belongs to significant environmental stressors (Huber, 1972; Cimboláková et al, 2019) which affect the algae functioning and their key role in the photosynthesis
Effects on Dunaliella autofluorescence were evaluated from multichannel confocal images, while comparing the intensities captured in the two channels covering the green and the red regions of the visible spectrum separately
Gathered results demonstrate novel findings: for the first time, differential responsiveness of endogenous fluorescence of marine algae Dunaliella to selected environmental stressors is shown in the flagella vs. the body region separately
Summary
Acid rains, together with modification of illumination conditions belongs to significant environmental stressors (Huber, 1972; Cimboláková et al, 2019) which affect the algae functioning and their key role in the photosynthesis. Monitoring rapid responsiveness of the algae fluorescence under environmental stressors presents non-invasive approach in order to understand underlying metabolic changes in stressed living cells which is a prerequisite for understanding their pathophysiological changes. Among the brightest endogenous fluorophores (autofluorescence) inside biological tissue are chlorophylls in plants (Govindjee Papageorgiou and Rabinowitch, 1967) and NADP(H) and flavins in mitochondria (Chorvatova and Chorvat, 2014). These molecules are the main electron donors and acceptors in the biochemical processes such as photosynthesis, or oxidative phosphorylation. Presence of a stressor-sensitive green fluorescence was recorded in Dunaliella algae under heavy metal of cadmium (Ivoševic DeNardis et al, 2019). Increase in the autofluorescence related to flavoproteins, derived both from oxidation and synthesis of flavins was described in prokaryotic, as well as eukaryotic cells, mainly when experiencing severe life-threatening stress (Surre et al, 2018)
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