Circadian and diurnal calcium oscillations encode photoperiodic information in Arabidopsis

We have tested the hypothesis that circadian oscillations in the concentration of cytosolic free calcium ([Ca2+](cyt)) can encode information. We imaged oscillations of [Ca2+](cyt) in the cotyledons and leaves of Arabidopsis (Arabidopsis thaliana) that have a 24-h period in light/dark cycles and also constant light. The amplitude, phase, and shape of the oscillations of [Ca2+](cyt) and [Ca2+](cyt) at critical daily time points were controlled by the light/dark regimes in which the plants were grown. These data provide evidence that 24-h oscillations in [Ca2+](cyt) encode information concerning daylength and light intensity, which are two major regulators of plant growth and development.