Entrainment and Phase-Shifting of the Circadian Rhythm of Cell Division by Calcium in Synchronous Cultures of the Wild-Type Z Strain and of the ZC Achlorophyllous Mutant of Euglena gracilis

Abstract

Cell division in exponentially increasing populations of the wildtype, photosynthetic Z strain of Euglena gracilis Klebs cultured autotrophically on an aerated, magnetically stirred, minimal mineral medium (pH 7.0) in constant light (LL) or in a light-dark 1 hour:1 hour cycle (LD:1,1) at 250C could be synchronized by a 10-hour:10-hour low (2 micromolar):normal (200 micromolar Since intracellular free calcium is well known as a cell regulator, coordinating many kinds of intracellular reactions and even its own concentration (1,2,5,7), it is quite possible that it may play a significant role in the functioning of circadian clocks (10, 13). Indeed, it has been demonstrated in a variety of eukaryotic organisms that circadian rhythmicity of many different types of physiological processes are modulated by calcium levels: cell shape (23, 24) cell division (18) in Euglena gracilis, ocular rhythms in Bulla gouldiana (25), leaf movement in Trifolium repens (3) and Cassiafasciculata (29), conidiation in Neurospora crassa (27), and phototaxis in Chlamydomonas reinhardtii (17). Three models for circadian oscillators (10) that are based in part on cellular calcium (18,21,22) share in common a cycling ofintracellular calcium among compartments (endoplasmic reticulum, mitochondria, cytoplasm, extracellular medium-depending on the model). Although this intercompartmental calcium cycling in itself constitutes the circadian mechanism in the Kippert model (21), it is only one important element of a biochemical circadian loop in that of Goto et al. (18).In an attempt to elucidate the role of calcium in the timing mechanisms that are responsible for circadian periodicities, we have studied the effects of changes in extracellular calcium concentration on the rhythm of cell division in E. gracilis Klebs. Such changes affect the intracellular distribution of calcium via changes at the level of the plasma membrane as well as within another cellular compartment in this unicellular alga (35).

Chlamydomonas reinhardtii: duration of its cell cycle and phases at growth rates affected by light intensity

“…Similarly, the circadian oscillator was implicated in the gating of commitment to different cell cycle transitions (Hagiwara et al 2002) and in G2 arrest during cell population growth (Bolige et al 2005). Euglena gracilis is a very peculiar organism capable of surviving and thriving even when the chloroplast is lost (Tamponnet and Edmunds 1990); moreover, the circadian regulation seems to be more pronounced if the chloroplast is lost (Tamponnet and Edmunds 1990). Therefore, it would be interesting to compare its molecular mechanism of circadian regulation with that of other organisms, particularly Chlamydomonas reinhardtii.…”

Genetics of Circadian Rhythms

“…Edmunds and colleagues have applied a photosynthesis-deficient variant, ZC, that is completely devoid of chloro plasts (13,78,133). Edmunds and colleagues have applied a photosynthesis-deficient variant, ZC, that is completely devoid of chloro plasts (13,78,133).…”

Thylakoid-bound proteolytic activity against LHC II apoprotein in bean

“…The association of the protease on thylakoids might be affected by phytochrome photoreception via the changes in efflux and mobilization of cations (e.g. Ca++), known to follow Pr to Pfr transformation (Tamponnet andEdmunds 1990, Chae et al 1990). V/a such cation concentration changes, Pfr may similarly affect the oscillations in the degrading activity of thylakoids obtained from etiolated leaves following a Red light pulse.…”

“…Pfr, the biologically active phytochrome form, is known to induce influx and mobilization of Ca ++ in the cell (Tamponnet and Edmunds 1990;Chae et al 1990). Isolated intact chloroplasts were incubated in Tricine-NaOH, pH 7.3, supplemented or not with 5 mM MgCI2, and after lysis the stroma was separated from thylakoids by centrifugation.…”