Improvement of ionizing gamma irradiation tolerance of Chlorella vulgaris by pretreatment with polyethylene glycol

Abstract

Purpose: To evaluate the effects of polyethylene glycol (PEG) 6000 pretreatment on growth and physiological responses of eukaryotic microalga Chlorella vulgaris exposed to ionizing irradiation.

Materials and methods: The microalgal cells pretreated with different PEG concentrations (0, 5, 10 and 20%) and then exposed to 300 Gray gamma irradiation at a dose rate of 0.5 Gy s⁻¹. The various growth and physiological parameters including algal growth, cell size, the degree of electrolyte leakage (EL) and lipid peroxidation, the content of pigments and proline and the activity of antioxidant enzymes under gamma-free or 300 Gray gamma irradiation conditions were examined.

Results: The results showed that PEG stimulated a higher growth and cell size under both stress-free and gamma-stress conditions. The maximum growth and cell size was reported when the algae was pretreated with 10% PEG. A relative increase of catalase activity was observed in all samples after exposing to gamma irradiation. However, the highest value was recorded for the gamma-radiated algae pretreated with 10% PEG. In the absence of PEG, gamma irradiation induced a significant reduction in ascorbate peroxidase activity, but with PEG pretreatment, the enzyme activity remained constant or even increased after gamma irradiation. On the other hand, although gamma irradiation stress generally suppressed the activity of superoxide dismutase in all cells, pretreating the algae with PEG could diminish this suppressing effect at all applied concentrations. Compared to the PEG-free controls, a lower rate of chlorophylls and membrane integrity loss was shown in the PEG-treated algae when exposed to gamma stress. Total carotenoid content in PEG-treated algae was also similar under both gamma-free and gamma-radiated conditions. A PEG-independent increase in proline accumulation was reported under gamma-irradiation treatment.

Conclusions: Overall, the results suggested that PEG pretreatment could improve gamma-irradiation tolerance in C. vulgaris probably by stimulating a range of enzymatic and non-enzymatic reactive oxygen species scavenging systems. The microalgae may also consume PEG to break down and use it as an alternative source of carbon during stress which should be further studied in detail.

Keywords:

• Chlorella vulgaris microalgae
• polyethylene glycol
• gamma irradiation stress

Disclosure statement

The authors declare that they have no conflict of interest. The authors thank research fellows at Biotechnology lab of University of Kashan and Plant physiology lab of University of Payame Noor Ardestan for their technical supports and suggestion.

Additional information

Funding

This work was supported by graduate study of University of Kashan under grant no. 6538/27825.

Notes on contributors

Seyed Ali Hosseini Tafreshi

Seyed Ali Hosseini Tafreshi, is an Assistant Professor in the Department of cell and molecular biology, Faculty of chemistry, University of Kashan. Her research field is biotechnology and molecular biology of plants and microalgae.

Peyman Aghaie

Peyman Aghaie, is an Assistant Professor in the Department of Biology, Payame Noor Universtiy. Her research is concentrated on plant and algal physiology.

Mohammad Amin Toghyani

Mohammad Amin Toghyani, having her area of expertise in the research field of biological effects of different stresses on plants and microalgae.

Ahmad Ramazani-Moghaddam-Arani

Ahmad Ramazani-Moghaddam-Arani, is an Associate Professor in the Department of Nuclear Physics, Faculty of Physics, University of Kashan.