Catalyzing Initial Responses to Environmental Stresses.

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