CIRCADIAN OSCILLATIONS OF CYTOSOLIC AND CHLOROPLASTIC FREE CALCIUM INPLANTS

Tobacco and Arabidopsis plants, expressing a transgene for the calcium -sensitive luminescent protein apoaequorin, revealed circadian oscilla tions in free cytosolic calcium that can be phase-shifted by light-dar k signals. When apoaequorin was targeted to the chloroplast, circadian chloroplast calcium rhythms were likewise observed after transfer of the seedlings to constant darkness. Circadian oscillations in free cal cium concentrations can be expected to control many calcium-dependent enzymes and processes accounting for circadian outputs. Regulation of calcium flux is therefore fundamental to the organization of circadian systems.