Abstract
Calcium ion (Ca^<2+>) acts as a second messenger in plants. Cold stress causes cytosolic Ca^<2+> elevation, which is expected to act as a signal to finally regulate gene expression. Because transient elevation of cytosolic Ca^<2+> concentration was observed in cold stress but the detail is still unknown, we developed an experimental system to detect intracellular Ca^<2+> dynamics with the combination of the confocal cryomicroscopy and Ca^<2+>-sensitive fluorescent probe, Yellow Cameleon 3.6, which is a fluorescence resonance energy transfer (FRET)-based Ca^<2+> sensor. This system can detect changes in cytosolic Ca^<2+> concentration in living Arabidopsis roots in a non-destructive way. Using this system, we observed Ca^<2+> signals at three cooling rates: 2℃/min, 4℃/min and 8℃/min. A faster cooling rate resulted in a higher and more rapid peak elevation of cytosolic Ca^<2+>, suggesting that cooling rate is a key factor in the temperature sensing mechanism. By the same token, it is inferred that the sensing of cooling rate in plant cells may lead to changes in gene expression appropriate to temperature changes.
