The unicellular green microalga Chlamydomonas reinhardtii is a model eukaryotic organism for studying the processes of photosynthesis, cell motility, carbon nutrition, protein biosynthesis and the development of new biotechnological regulations. As a carbon source for heterotrophic or mixotrophic growth, C. reinhardtii is capable to use acetate. The aim of this work was to study the effect of piracetam (2-(2-oxypyrolidin-1-il)acetamide) as a possible biostimulant of plant organisms on growth and the photosynthetic characteristics of C. reinhardtii cells. Cumulative cultures of C. reinhardtii were grown under mixotrophic conditions on liquid medium, illuminated with LED lamps with a light flux density of 100 µmol photons · m–2 · s–1 with the addition of piracetam to a concentration of 0.2—0.8 mg/ml. The growth rate of the culture was estimated by the increase of cells number in the culture medium. The toxic effect of Сu and Zn was studied after adding zinc and copper sulphates at a concentration of 10 mg/ml and 20 mg/ml, respectively, to the culture medium in the mid-exponential growth phase of the culture. O2 concentration was determined by the amperometric method using a Clark platinum electrode. The functional state of the photosynthetic apparatus was assessed by determining the parameters of the chlorophyll fluorescence induction curve with the XE-PAM fluorimeter (Walz, Germany). The intensity of actinic light corresponded to the intensity of illumination during the cultivation of algae. The results showed that the addition of piracetam to the culture medium led to an increase in the efficiency of photosynthesis, which was accompanied by an increase in the rate of O2 evolution in the light and stimulation of C. reinhardtii growth. In the presence of piracetam (0.4 mg/ml) in the cultural medium, the cell concentration after 10 days of growth increased by 65 % as compared with the control. Piracetam stimulated culture growth in the presence of toxic concentrations of ZnSO4, providing a stress-protective effect.
Keywords: Chlamydomonas reinhardtii, piracetam, photosynthesis, growth, heavy metals, biostimulants
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