Physiological stabilization of Euglena gracilis cells by high extracellular calcium (100 mM)

Experiments were performed to test whether or not high concentrations of CaCl2 (100 mM) are able to arrest and stabilize internal structures and associated functions in Euglena gracilis Z cells stored in darkness at 4 degrees C. Storage of photoheterotrophically grown green cells in high Ca2+ media (2-100 mM) retards pheophytinization of the chlorophylls, preserves photosynthetic activities and stabilizes the structural organization of the associated light-harvesting complexes of the photosystem II units. Alterations of photosynthesis and respiration by chlorpromazine or by temperature are strongly reduced in cells stored under such conditions. More precisely, a chlorpromazine inhibition site is evidenced in the mitochondrial electron pathway and its location in the chloroplastic electron pathway is clarified. Adaptation of Euglena cells from 2 mM to 100 mM Ca2+ medium is accompanied by an increase both in the externally bound and total internal calcium concentration. A mechanism involving a Ca2+ deposit on internal membranes is proposed. Such interpretation is extended to the storage of cells immobilized in Ca2+-alginate gel.