COMBINED EFFECT OF CADMIUM AND LOWERED SALINITY ON DYNAMICS OF ABUNDANCE AND PHYSIOLOGICAL PROCESSES FOR ALGA PLAGIOSELMIS PROLONGA

Combined effect of cadmium (10, 30, and 50 mg/L) and salinity (32, 24, and 16 ‰) on marine unicellular alga Plagioselmis prolonga (Cryptophyta) is investigated. Such parameters as the cells number dynamics, their size, side scattering (as a characteristic of internal structure of cells), photosynthetic pigments fluorescence (chlorophyll a, phycoerythrin, allophycocyanin, as a measure of the photosynthetic apparatus function), and reactive oxygen species (ROS) content (as an index of the cellular membranes destruction) were registered in experiments using the flow cytometer CytoFLEX (Beckman Coulter). Addition of cadmium in concentration of 10 mg/L to the water with salinity 32 ‰ did not influence on alga growth and its physiological parameters. The higher concentrations of cadmium, as 30 and 50 mg/L, stimulated the cells growth and ROS increased under the concentration of 50 mg/L, but other parameters did not altered. The same contamination with cadmium under salinity 24 ‰ caused the cells size rising and their intensive growth, ROS increasing on 3rd day and decreasing on 7th day of exposition, and phycoerythrin and allophycocyanin fluorescence diminishing, but the side scattering and chlorophyll a fluorescence still did not differ from the control. Any concentration of cadmium in the water with salinity 16 ‰ caused the population growth inhibition, decreasing of side scattering and all photosynthetic pigments fluorescence, and increasing of ROS and cells size. There is concluded that cadmium contamination in conditions of normal (32 ‰) salinity has a stimulation effect on Plagioselmis prolonga growth and no effect on its photosynthetic apparatus, but the same contamination in conditions of lowered salinity has a negative effect on both its growth and photosynthetic functions, whereas the reactive oxygen species content increases and the cells become larger under the cadmium contamination regardless the salinity factor.