Effects of Ca2+ on the growth of Dunaliella tertiolecta in media with high concentrations of Mg2+
The growth rate of Dunaliella tertiolecta in a high MgSO4 (0.94 M) medium was lower than that in a NaCl medium of the same osmolality. Growth inhibition of D. tertiolecta in the high MgSO4 medium was partially relieved in response to increases in extracellular Ca2+ concentrations (1 – 11 mM). This growth recovery effect by supplemental Ca2+ was eliminated by the simultaneous additions of ethylene glycol-bis-(β-aminoethyl ether)-N′,N′-tetraacetic acid. The measurements of intracellular cations revealed that the intracellular concentration of Ca2+ increased with increases in the extracellular Ca2+ concentration. From the kinetic analysis of the relationship between the extracellular Ca2+ concentration and the growth in media containing various concentrations of Mg2+, Ca2+ was found to interact competitively with Mg2+ with regard to growth of D. tertiolecta in MgSO4 media. These results indicate that high concentrations of Mg2+ inhibit the uptake of Ca2+ into cells, resulting in the observed growth inhibition in MgSO4 media. Key words: Dunaliella, magnesium, calcium, antagonistic effect.