The calcium rhythms of different cell types oscillate with different circadian phases

Transgenic tobacco (Nicotiana plumbaginifolia) seedlings containing the Ca2 +-sensitive luminescent protein aequorin have been shown to exhibit circadi an variations in cytosolic calcium. Concomitant measurements of cytosolic a nd nuclear calcium show that circadian variations in the cytoplasm are not expressed in the nucleus. To investigate whether all cells of transgenic se edlings contribute equally to circadian variations in cytosolic calcium, di fferent promoters eliciting different expression patterns have been placed upstream of aequorin and used for transformation. The circadian peak occurr ed at different times in the three transgenic lines constructed. Luminescen ce imaging of these transgenic lines indicated that aequorin was differenti ally accumulated among the main tissues and cells of the seedlings and over coat technology with applied epidermal strips indicated that the surface ce ll layers contribute the vast majority of luminescent light. We conclude th at the Ca2+ rhythmicities of cells and tissues oscillate with distinct diff erences in phase, that this might represent different underlying cellular c ontrol mechanisms and that these observations have significant implications for our understanding and study of Ca2+ mediated signal transduction in pl ant cells.