MAGNESIUM STARVED CELLS OF EUGLENA-GRACILIS - A POSSIBLE MODEL SYSTEMFOR STUDYING MG2+ INFLUX

In order to obtain a model which allows to directly study Mg2+ influx into the cell, Mg2+ deficiency was induced in the unicellular photoaut otrophic flagellate Euglena gracilis. Lack of Mg2+ in the culture medi um leads to a number of morphological, biochemical, and physiological changes in Euglena gracilis. The rate of cell division was reduced und er Mg2+-free conditions. Subsequently an enlargement of the cells was observed and they changed from spindle-like to oval shape. The Mg2+-st arved cells were well filled with paramylon granules, while their moti lity 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 ma nnose on the cell surface rose in the Mg2+-starved cultures, shown in a lectin-binding assay. Fucose was found on the pellicle of Mg2+-starv ed cells only. Cultivation of Euglena gracilis in Mg2+-free medium ind uced a drastic reduction of the intracellular Mg2+ concentration alrea dy after 24 h (from 233 nmol/10(6) cells to 82 nmol/10(6) cells). When Mg2+ was made available again, the Mg2+-starved cells took them up ra pidly and the intracellular concentration of free Mg2+ rose. As Mg2+ d epletion could be induced in Euglena gracilis easily by manipulating t he culture conditions and as the cells remained viable, it was conclud ed that this flagellate can be used as a model organism for studying t he Mg2+ uptake of eukaryotic cells.