Ca2+talyzing Initial Responses to Environmental Stresses.

Plants have evolved stress-sensing machineries that initiate rapid adaptive environmental stress responses. Cytosolic calcium ion (Ca2+) is the most prominent second messenger that couples extracellular signals with specific intracellular responses. Essential early events that generate a cytosolic Ca2+ spike in response to environmental stress are starting to emerge. We review sensory machineries, including ion channels and transporters, which perceive various stress stimuli and allow cytosolic Ca2+ influx. We highlight integrative roles of Ca2+ channels in plant responses to various environmental stresses, as well as possible interplay of Ca2+ with other early signaling components, which facilitates signal propagation for systemic spread and spatiotemporal variations in respect to external cues. The early Ca2+ signaling schemes inspire the identification of additional stress sensors.