Aequorin-based luminescence imaging reveals stimulus- and tissue-specific Ca2+ dynamics in Arabidopsis plants.

Calcium ion is a versatile second messenger for diverse cell signaling in response to developmental and environmental cues. The specificity of Ca(2+)-mediated signaling is defined by stimulus-elicited Ca(2+) signature and downstream decoding processes. Here, an Aequorin-based luminescence recording system was developed for monitoring Ca(2+) in response to various stimuli in Arabidopsis. With the simple, highly sensitive, and robust Ca(2+) recording, this system revealed stimulus- and tissue-specific Ca(2+) signatures in seedlings. Cellular Ca(2+) dynamics and relationship to Aequorin-based Ca(2+) recording were explored using a GFP-based Ca(2+) indicator, which suggested that a synchronous cellular Ca(2+) signal is responsible for cold-induced Ca(2+) response in seedlings, whereas asynchronous Ca(2+) oscillation contributes to osmotic stress-induced Ca(2+) increase in seedlings. The optimized recording system would be a powerful tool for the identification and characterization of novel components in Ca(2+)-mediated stress-signaling pathways.