Magnesium Starved Cells of Euglena gracilis - a Possible Model System for Studying Mg2+ Influx?

Euglena gracilis, Nutrition, Magnesium Deficiency, Magnesium Transport In order to obtain a model which allows to directly study Mg2+ influx into the cell, Mg2+ deficiency was induced in the unicellular photoautotrophic flagellate Euglena gracilis. Lack of Mg2+ in the culture medium leads to a number of morphological, biochemical, and physio­ logical changes in Euglena gracilis. The rate of cell division was reduced under Mg2+-free conditions. Subsequently an enlargement of the cells was observed and they changed from spindle-like to oval shape. The Mg2+-starved cells were well filled with paramylon granules, while their motility and vitality was not impaired. Concurrently with the larger cell size the protein-, carbohydrate-, and chlorophyll content of the cells increased. Further changes were observed in the surface carbohydrates. The proportion of cells with galactose, N-acetyl-galactosamine and mannose on the cell surface rose in the Mg2+-starved cultures, shown in a lectin-binding assay. Fucose was found on the pellicle of Mg2+-starved cells only. Cultivation of Euglena gracilis in Mg2+-free medium induced a drastic reduction of the intracellular Mg2+ concentration already after 24 h (from 233 nmol/106 cells to 82 nmol/106 cells). When Mg2+ was made available again, the Mg2+-starved cells took them up rapidly and the intracellular concentration of free Mg2+ rose. As Mg2+ depletion could be induced in Euglena gracilis easily by manipulating the culture conditions and as the cells remained viable, it was con­ cluded that this flagellate can be used as a model organism for studying the Mg2+ uptake of eukaryotic cells.