Comprehensive analysis of copper ions effect on the primary processes of photosynthesis in Scenedesmus quadricauda based on chlorophyll a fluorescence measurements in suspension and on single cells

Pirutin S.K., Shank M.A., Jia S., Konuhov I.V., Todorenko D.A., Chervitsov R.N., Fursova P.V., Kabashnikova L.F., Plusnina T.Yu., Khruschev S.S., Riznichenko G.Yu., Rubin A.B.
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The effect of copper ions on the primary processes of photosynthesis in freshwater microalgae Scenedesmus quadricauda was studied using a set of biophysical and mathematical methods. Chlorophyll a fluorescence transients were recorded both in cell suspensions and at the level of single cells after incubation at copper concentrations of 0.1–10 $\mu$M under light and dark conditions. It was found that copper has a dose-dependent effect on the photosynthetic apparatus of microalgae. At low copper concentration (0.1 $\mu$M), a stimulating effect on a number of studied parameters was observed, whereas significant disruption of Photosystem II activity was detected at 10 $\mu$M. The method of analyzing fluorescence of single cells proved to be more sensitive compared to traditional suspension measurements, allowing the detection of heterogeneous cellular responses to the toxicant. Analysis of chlorophyll a fast fluorescence kinetics showed that the JIP-test parameters $\delta_{Ro}$ and $\varphi_{Ro}$ were the most sensitive to copper exposure and were significantly different from the control when exposed not only to high but also to medium (1 $\mu$M) copper concentrations. The decrease in photochemical activity of cells during light incubation was less pronounced compared to dark conditions. The application of data normalization to optical density at $\lambda = 455$ nm significantly increased the sensitivity of the method and accuracy of result interpretation. The use of L1-regularization (LASSO) by the least angles method (LARS) for the spectral multi-exponential approximation of the fluorescence transients allowed us to reveal their temporal characteristics. Mathematical analysis of the obtained data suggested that copper exposure leads to increased non-photochemical quenching of fluorescence, which serves as a protective mechanism for dissipating excess excitation energy. The revealed heterogeneity of cellular responses to copper action may have important ecological significance, ensuring the survival of part of the population under stress conditions. The obtained data confirm the promise of using fluorescent analysis methods for early diagnosis of heavy metal stress effects on photosynthesizing organisms.

Keywords: Scenedesmus quadricauda, copper ions (Cu2+), chlorophyll fluorescence, photosystem II (PSII), JIP-test, photochemical quantum yield $\left(\frac{F_\nu}{F_m}\right)$, microfluorimetry, nonphotochemical quenching, data normalization, spectral multi-exponential approximation
Citation in English: Pirutin S.K., Shank M.A., Jia S., Konuhov I.V., Todorenko D.A., Chervitsov R.N., Fursova P.V., Kabashnikova L.F., Plusnina T.Yu., Khruschev S.S., Riznichenko G.Yu., Rubin A.B. Comprehensive analysis of copper ions effect on the primary processes of photosynthesis in Scenedesmus quadricauda based on chlorophyll a fluorescence measurements in suspension and on single cells // Computer Research and Modeling, 2025, vol. 17, no. 2, pp. 293-322
Citation in English: Pirutin S.K., Shank M.A., Jia S., Konuhov I.V., Todorenko D.A., Chervitsov R.N., Fursova P.V., Kabashnikova L.F., Plusnina T.Yu., Khruschev S.S., Riznichenko G.Yu., Rubin A.B. Comprehensive analysis of copper ions effect on the primary processes of photosynthesis in Scenedesmus quadricauda based on chlorophyll a fluorescence measurements in suspension and on single cells // Computer Research and Modeling, 2025, vol. 17, no. 2, pp. 293-322
DOI: 10.20537/2076-7633-2025-17-2-293-322
URL: http://crm-en.ics.org.ru/journal/article/3606/

 

Supplementary information:

 

Spectral multi-exponential approximation of chlorophyll a fluorescence transients of microalgae Scenedesmus quadricauda culture after incubation with copper ions under various conditions

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