In plants,Ca2+ signals occur in response to both environmental and developmental stimuli.These signals involve increases in [Ca2+] in compartments such as the cytoplasm,nucleus,and mitochondria,and can display multiple shapes ranging from single transients to repetitive Ca2+ oscillations.Generation and shaping of stimulus specific [Ca2+] signatures depends on Ca2+ influxes and effluxes occurring at both the plasma membrane (PM) and membranes of the different subcellular compartments.An elaborate toolkit of Ca2+ relay and Ca2+ sensor proteins likely contributes to decoding these Ca2+ signals into specific cellular and organismic response reactions (Kudla et al.,2010).From its very beginning,research on Ca2+ signaling in plants has relied on sophisticated approaches to monitor Ca2+ dynamics in vivo.While the first reports on [Ca2+]cyt changes in Chara and in higher plants in the 1980s were based on the injection of recombinant aequorin Ca2+ reporter proteins or the application of Ca2+-selective microelectrodes,Ca2+ signaling research during the following decade was dominated by the use of improved ratiometric fluorescent chemical dyes (reviewed in Brownlee,2000;Swanson et al.,2011;Batisti(c) and Kudla,2012).However,more recently,the invention of genetically encoded Ca2+ indicators (GECIs) and the development of novel imaging tools have enabled the study of Ca2+ dynamics in many plant cell types and organs in non-preceded spatial and temporal resolution.Quite excitingly,we are currently witnessing another revolution in advancing the GECIs and imaging techniques that would dramatically enhance our understanding of Ca2+ signals in many biological processes.